diff --git a/Gemfile b/Gemfile
index afed1ac94..e869e5f7a 100644
--- a/Gemfile
+++ b/Gemfile
@@ -29,9 +29,7 @@ gem 'addressable', '~> 2.8'
 gem 'bootsnap', '~> 1.10.2', require: false
 gem 'browser'
 gem 'charlock_holmes', '~> 0.7.7'
-gem 'iso-639'
 gem 'chewy', '~> 7.2'
-gem 'cld3', '~> 3.4.4'
 gem 'devise', '~> 4.8'
 gem 'devise-two-factor', '~> 4.0'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 5ecddec12..f7dd292dd 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -152,8 +152,6 @@ GEM
       elasticsearch (>= 7.12.0, < 7.14.0)
       elasticsearch-dsl
     chunky_png (1.4.0)
-    cld3 (3.4.4)
-      ffi (>= 1.1.0, < 1.16.0)
     climate_control (0.2.0)
     coderay (1.1.3)
     color_diff (0.1)
@@ -301,7 +299,6 @@ GEM
       terminal-table (>= 1.5.1)
     idn-ruby (0.1.4)
     ipaddress (0.8.3)
-    iso-639 (0.3.5)
     jmespath (1.5.0)
     json (2.5.1)
     json-canonicalization (0.3.0)
@@ -698,7 +695,6 @@ DEPENDENCIES
   capybara (~> 3.36)
   charlock_holmes (~> 0.7.7)
   chewy (~> 7.2)
-  cld3 (~> 3.4.4)
   climate_control (~> 0.2)
   color_diff (~> 0.1)
   concurrent-ruby
@@ -725,7 +721,6 @@ DEPENDENCIES
   httplog (~> 1.5.0)
   i18n-tasks (~> 0.9)
   idn-ruby
-  iso-639
   json-ld
   json-ld-preloaded (~> 3.2)
   kaminari (~> 1.2)
diff --git a/app/helpers/languages_helper.rb b/app/helpers/languages_helper.rb
index 730724208..f3ed7b314 100644
--- a/app/helpers/languages_helper.rb
+++ b/app/helpers/languages_helper.rb
@@ -1,94 +1,237 @@
 # frozen_string_literal: true
 
 module LanguagesHelper
-  HUMAN_LOCALES = {
-    af: 'Afrikaans',
-    ar: 'العربية',
-    ast: 'Asturianu',
-    bg: 'Български',
-    bn: 'বাংলা',
-    br: 'Breton',
-    ca: 'Català',
-    co: 'Corsu',
-    cs: 'Čeština',
-    cy: 'Cymraeg',
-    da: 'Dansk',
-    de: 'Deutsch',
-    el: 'Ελληνικά',
-    en: 'English',
-    eo: 'Esperanto',
+  ISO_639_1 = {
+    aa: ['Afar', 'Afaraf'].freeze,
+    ab: ['Abkhaz', 'аҧсуа бызшәа'].freeze,
+    ae: ['Avestan', 'avesta'].freeze,
+    af: ['Afrikaans', 'Afrikaans'].freeze,
+    ak: ['Akan', 'Akan'].freeze,
+    am: ['Amharic', 'አማርኛ'].freeze,
+    an: ['Aragonese', 'aragonés'].freeze,
+    ar: ['Arabic', 'اللغة العربية'].freeze,
+    as: ['Assamese', 'অসমীয়া'].freeze,
+    av: ['Avaric', 'авар мацӀ'].freeze,
+    ay: ['Aymara', 'aymar aru'].freeze,
+    az: ['Azerbaijani', 'azərbaycan dili'].freeze,
+    ba: ['Bashkir', 'башҡорт теле'].freeze,
+    be: ['Belarusian', 'беларуская мова'].freeze,
+    bg: ['Bulgarian', 'български език'].freeze,
+    bh: ['Bihari', 'भोजपुरी'].freeze,
+    bi: ['Bislama', 'Bislama'].freeze,
+    bm: ['Bambara', 'bamanankan'].freeze,
+    bn: ['Bengali', 'বাংলা'].freeze,
+    bo: ['Tibetan', 'བོད་ཡིག'].freeze,
+    br: ['Breton', 'brezhoneg'].freeze,
+    bs: ['Bosnian', 'bosanski jezik'].freeze,
+    ca: ['Catalan', 'Català'].freeze,
+    ce: ['Chechen', 'нохчийн мотт'].freeze,
+    ch: ['Chamorro', 'Chamoru'].freeze,
+    co: ['Corsican', 'corsu'].freeze,
+    cr: ['Cree', 'ᓀᐦᐃᔭᐍᐏᐣ'].freeze,
+    cs: ['Czech', 'čeština'].freeze,
+    cu: ['Old Church Slavonic', 'ѩзыкъ словѣньскъ'].freeze,
+    cv: ['Chuvash', 'чӑваш чӗлхи'].freeze,
+    cy: ['Welsh', 'Cymraeg'].freeze,
+    da: ['Danish', 'dansk'].freeze,
+    de: ['German', 'Deutsch'].freeze,
+    dv: ['Divehi', 'Dhivehi'].freeze,
+    dz: ['Dzongkha', 'རྫོང་ཁ'].freeze,
+    ee: ['Ewe', 'Eʋegbe'].freeze,
+    el: ['Greek', 'Ελληνικά'].freeze,
+    en: ['English', 'English'].freeze,
+    eo: ['Esperanto', 'Esperanto'].freeze,
+    es: ['Spanish', 'Español'].freeze,
+    et: ['Estonian', 'eesti'].freeze,
+    eu: ['Basque', 'euskara'].freeze,
+    fa: ['Persian', 'فارسی'].freeze,
+    ff: ['Fula', 'Fulfulde'].freeze,
+    fi: ['Finnish', 'suomi'].freeze,
+    fj: ['Fijian', 'Vakaviti'].freeze,
+    fo: ['Faroese', 'føroyskt'].freeze,
+    fr: ['French', 'Français'].freeze,
+    fy: ['Western Frisian', 'Frysk'].freeze,
+    ga: ['Irish', 'Gaeilge'].freeze,
+    gd: ['Scottish Gaelic', 'Gàidhlig'].freeze,
+    gl: ['Galician', 'galego'].freeze,
+    gu: ['Gujarati', 'ગુજરાતી'].freeze,
+    gv: ['Manx', 'Gaelg'].freeze,
+    ha: ['Hausa', 'هَوُسَ'].freeze,
+    he: ['Hebrew', 'עברית'].freeze,
+    hi: ['Hindi', 'हिन्दी'].freeze,
+    ho: ['Hiri Motu', 'Hiri Motu'].freeze,
+    hr: ['Croatian', 'Hrvatski'].freeze,
+    ht: ['Haitian', 'Kreyòl ayisyen'].freeze,
+    hu: ['Hungarian', 'magyar'].freeze,
+    hy: ['Armenian', 'Հայերեն'].freeze,
+    hz: ['Herero', 'Otjiherero'].freeze,
+    ia: ['Interlingua', 'Interlingua'].freeze,
+    id: ['Indonesian', 'Bahasa Indonesia'].freeze,
+    ie: ['Interlingue', 'Interlingue'].freeze,
+    ig: ['Igbo', 'Asụsụ Igbo'].freeze,
+    ii: ['Nuosu', 'ꆈꌠ꒿ Nuosuhxop'].freeze,
+    ik: ['Inupiaq', 'Iñupiaq'].freeze,
+    io: ['Ido', 'Ido'].freeze,
+    is: ['Icelandic', 'Íslenska'].freeze,
+    it: ['Italian', 'Italiano'].freeze,
+    iu: ['Inuktitut', 'ᐃᓄᒃᑎᑐᑦ'].freeze,
+    ja: ['Japanese', '日本語'].freeze,
+    jv: ['Javanese', 'basa Jawa'].freeze,
+    ka: ['Georgian', 'ქართული'].freeze,
+    kg: ['Kongo', 'Kikongo'].freeze,
+    ki: ['Kikuyu', 'Gĩkũyũ'].freeze,
+    kj: ['Kwanyama', 'Kuanyama'].freeze,
+    kk: ['Kazakh', 'қазақ тілі'].freeze,
+    kl: ['Kalaallisut', 'kalaallisut'].freeze,
+    km: ['Khmer', 'ខេមរភាសា'].freeze,
+    kn: ['Kannada', 'ಕನ್ನಡ'].freeze,
+    ko: ['Korean', '한국어'].freeze,
+    kr: ['Kanuri', 'Kanuri'].freeze,
+    ks: ['Kashmiri', 'कश्मीरी'].freeze,
+    ku: ['Kurdish', 'Kurdî'].freeze,
+    kv: ['Komi', 'коми кыв'].freeze,
+    kw: ['Cornish', 'Kernewek'].freeze,
+    ky: ['Kyrgyz', 'Кыргызча'].freeze,
+    la: ['Latin', 'latine'].freeze,
+    lb: ['Luxembourgish', 'Lëtzebuergesch'].freeze,
+    lg: ['Ganda', 'Luganda'].freeze,
+    li: ['Limburgish', 'Limburgs'].freeze,
+    ln: ['Lingala', 'Lingála'].freeze,
+    lo: ['Lao', 'ພາສາ'].freeze,
+    lt: ['Lithuanian', 'lietuvių kalba'].freeze,
+    lu: ['Luba-Katanga', 'Tshiluba'].freeze,
+    lv: ['Latvian', 'latviešu valoda'].freeze,
+    mg: ['Malagasy', 'fiteny malagasy'].freeze,
+    mh: ['Marshallese', 'Kajin M̧ajeļ'].freeze,
+    mi: ['Māori', 'te reo Māori'].freeze,
+    mk: ['Macedonian', 'македонски јазик'].freeze,
+    ml: ['Malayalam', 'മലയാളം'].freeze,
+    mn: ['Mongolian', 'Монгол хэл'].freeze,
+    mr: ['Marathi', 'मराठी'].freeze,
+    ms: ['Malay', 'Bahasa Malaysia'].freeze,
+    mt: ['Maltese', 'Malti'].freeze,
+    my: ['Burmese', 'ဗမာစာ'].freeze,
+    na: ['Nauru', 'Ekakairũ Naoero'].freeze,
+    nb: ['Norwegian Bokmål', 'Norsk bokmål'].freeze,
+    nd: ['Northern Ndebele', 'isiNdebele'].freeze,
+    ne: ['Nepali', 'नेपाली'].freeze,
+    ng: ['Ndonga', 'Owambo'].freeze,
+    nl: ['Dutch', 'Nederlands'].freeze,
+    nn: ['Norwegian Nynorsk', 'Norsk nynorsk'].freeze,
+    no: ['Norwegian', 'Norsk'].freeze,
+    nr: ['Southern Ndebele', 'isiNdebele'].freeze,
+    nv: ['Navajo', 'Diné bizaad'].freeze,
+    ny: ['Chichewa', 'chiCheŵa'].freeze,
+    oc: ['Occitan', 'occitan'].freeze,
+    oj: ['Ojibwe', 'ᐊᓂᔑᓈᐯᒧᐎᓐ'].freeze,
+    om: ['Oromo', 'Afaan Oromoo'].freeze,
+    or: ['Oriya', 'ଓଡ଼ିଆ'].freeze,
+    os: ['Ossetian', 'ирон æвзаг'].freeze,
+    pa: ['Panjabi', 'ਪੰਜਾਬੀ'].freeze,
+    pi: ['Pāli', 'पाऴि'].freeze,
+    pl: ['Polish', 'Polski'].freeze,
+    ps: ['Pashto', 'پښتو'].freeze,
+    pt: ['Portuguese', 'Português'].freeze,
+    qu: ['Quechua', 'Runa Simi'].freeze,
+    rm: ['Romansh', 'rumantsch grischun'].freeze,
+    rn: ['Kirundi', 'Ikirundi'].freeze,
+    ro: ['Romanian', 'Română'].freeze,
+    ru: ['Russian', 'Русский'].freeze,
+    rw: ['Kinyarwanda', 'Ikinyarwanda'].freeze,
+    sa: ['Sanskrit', 'संस्कृतम्'].freeze,
+    sc: ['Sardinian', 'sardu'].freeze,
+    sd: ['Sindhi', 'सिन्धी'].freeze,
+    se: ['Northern Sami', 'Davvisámegiella'].freeze,
+    sg: ['Sango', 'yângâ tî sängö'].freeze,
+    si: ['Sinhala', 'සිංහල'].freeze,
+    sk: ['Slovak', 'slovenčina'].freeze,
+    sl: ['Slovenian', 'slovenščina'].freeze,
+    sn: ['Shona', 'chiShona'].freeze,
+    so: ['Somali', 'Soomaaliga'].freeze,
+    sq: ['Albanian', 'Shqip'].freeze,
+    sr: ['Serbian', 'српски језик'].freeze,
+    ss: ['Swati', 'SiSwati'].freeze,
+    st: ['Southern Sotho', 'Sesotho'].freeze,
+    su: ['Sundanese', 'Basa Sunda'].freeze,
+    sv: ['Swedish', 'Svenska'].freeze,
+    sw: ['Swahili', 'Kiswahili'].freeze,
+    ta: ['Tamil', 'தமிழ்'].freeze,
+    te: ['Telugu', 'తెలుగు'].freeze,
+    tg: ['Tajik', 'тоҷикӣ'].freeze,
+    th: ['Thai', 'ไทย'].freeze,
+    ti: ['Tigrinya', 'ትግርኛ'].freeze,
+    tk: ['Turkmen', 'Türkmen'].freeze,
+    tl: ['Tagalog', 'Wikang Tagalog'].freeze,
+    tn: ['Tswana', 'Setswana'].freeze,
+    to: ['Tonga', 'faka Tonga'].freeze,
+    tr: ['Turkish', 'Türkçe'].freeze,
+    ts: ['Tsonga', 'Xitsonga'].freeze,
+    tt: ['Tatar', 'татар теле'].freeze,
+    tw: ['Twi', 'Twi'].freeze,
+    ty: ['Tahitian', 'Reo Tahiti'].freeze,
+    ug: ['Uyghur', 'ئۇيغۇرچە‎'].freeze,
+    uk: ['Ukrainian', 'Українська'].freeze,
+    ur: ['Urdu', 'اردو'].freeze,
+    uz: ['Uzbek', 'Ўзбек'].freeze,
+    ve: ['Venda', 'Tshivenḓa'].freeze,
+    vi: ['Vietnamese', 'Tiếng Việt'].freeze,
+    vo: ['Volapük', 'Volapük'].freeze,
+    wa: ['Walloon', 'walon'].freeze,
+    wo: ['Wolof', 'Wollof'].freeze,
+    xh: ['Xhosa', 'isiXhosa'].freeze,
+    yi: ['Yiddish', 'ייִדיש'].freeze,
+    yo: ['Yoruba', 'Yorùbá'].freeze,
+    za: ['Zhuang', 'Saɯ cueŋƅ'].freeze,
+    zh: ['Chinese', '中文'].freeze,
+    zu: ['Zulu', 'isiZulu'].freeze,
+  }.freeze
+
+  ISO_639_3 = {
+    ast: ['Asturian', 'Asturianu'].freeze,
+    kab: ['Kabyle', 'Taqbaylit'].freeze,
+    kmr: ['Northern Kurdish', 'Kurmancî'].freeze,
+    zgh: ['Standard Moroccan Tamazight', 'ⵜⴰⵎⴰⵣⵉⵖⵜ'].freeze,
+  }.freeze
+
+  SUPPORTED_LOCALES = {}.merge(ISO_639_1).merge(ISO_639_3).freeze
+
+  # For ISO-639-1 and ISO-639-3 language codes, we have their official
+  # names, but for some translations, we need the names of the
+  # regional variants specifically
+  REGIONAL_LOCALE_NAMES = {
     'es-AR': 'Español (Argentina)',
     'es-MX': 'Español (México)',
-    es: 'Español',
-    et: 'Eesti',
-    eu: 'Euskara',
-    fa: 'فارسی',
-    fi: 'Suomi',
-    fr: 'Français',
-    ga: 'Gaeilge',
-    gd: 'Gàidhlig',
-    gl: 'Galego',
-    he: 'עברית',
-    hi: 'हिन्दी',
-    hr: 'Hrvatski',
-    hu: 'Magyar',
-    hy: 'Հայերեն',
-    id: 'Bahasa Indonesia',
-    io: 'Ido',
-    is: 'Íslenska',
-    it: 'Italiano',
-    ja: '日本語',
-    ka: 'ქართული',
-    kab: 'Taqbaylit',
-    kk: 'Қазақша',
-    kmr: 'Kurmancî',
-    kn: 'ಕನ್ನಡ',
-    ko: '한국어',
-    ku: 'سۆرانی',
-    lt: 'Lietuvių',
-    lv: 'Latviešu',
-    mk: 'Македонски',
-    ml: 'മലയാളം',
-    mr: 'मराठी',
-    ms: 'Bahasa Melayu',
-    nl: 'Nederlands',
-    nn: 'Nynorsk',
-    no: 'Norsk',
-    oc: 'Occitan',
-    pl: 'Polski',
     'pt-BR': 'Português (Brasil)',
     'pt-PT': 'Português (Portugal)',
-    pt: 'Português',
-    ro: 'Română',
-    ru: 'Русский',
-    sa: 'संस्कृतम्',
-    sc: 'Sardu',
-    si: 'සිංහල',
-    sk: 'Slovenčina',
-    sl: 'Slovenščina',
-    sq: 'Shqip',
     'sr-Latn': 'Srpski (latinica)',
-    sr: 'Српски',
-    sv: 'Svenska',
-    ta: 'தமிழ்',
-    te: 'తెలుగు',
-    th: 'ไทย',
-    tr: 'Türkçe',
-    uk: 'Українська',
-    ur: 'اُردُو',
-    vi: 'Tiếng Việt',
-    zgh: 'ⵜⴰⵎⴰⵣⵉⵖⵜ',
     'zh-CN': '简体中文',
     'zh-HK': '繁體中文（香港）',
     'zh-TW': '繁體中文（臺灣）',
-    zh: '中文',
   }.freeze
 
   def human_locale(locale)
     if locale == 'und'
       I18n.t('generic.none')
+    elsif (supported_locale = SUPPORTED_LOCALES[locale.to_sym])
+      supported_locale[1]
+    elsif (regional_locale = REGIONAL_LOCALE_NAMES[locale.to_sym])
+      regional_locale
     else
-      HUMAN_LOCALES[locale.to_sym] || locale
+      locale
     end
   end
+
+  def valid_locale_or_nil(str)
+    return if str.blank?
+
+    code, = str.to_s.split(/[_-]/) # Strip out the region from e.g. en_US or ja-JP
+
+    return unless valid_locale?(code)
+
+    code
+  end
+
+  def valid_locale?(locale)
+    SUPPORTED_LOCALES.key?(locale.to_sym)
+  end
 end
diff --git a/app/helpers/settings_helper.rb b/app/helpers/settings_helper.rb
index 23739d1cd..3d5592867 100644
--- a/app/helpers/settings_helper.rb
+++ b/app/helpers/settings_helper.rb
@@ -2,7 +2,7 @@
 
 module SettingsHelper
   def filterable_languages
-    LanguageDetector.instance.language_names.select(&LanguagesHelper::HUMAN_LOCALES.method(:key?))
+    LanguagesHelper::SUPPORTED_LOCALES.keys
   end
 
   def hash_to_object(hash)
diff --git a/app/lib/activitypub/activity/create.rb b/app/lib/activitypub/activity/create.rb
index 33998c477..ea8d146d4 100644
--- a/app/lib/activitypub/activity/create.rb
+++ b/app/lib/activitypub/activity/create.rb
@@ -112,7 +112,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
         url: @status_parser.url || @status_parser.uri,
         account: @account,
         text: converted_object_type? ? converted_text : (@status_parser.text || ''),
-        language: @status_parser.language || detected_language,
+        language: @status_parser.language,
         spoiler_text: converted_object_type? ? '' : (@status_parser.spoiler_text || ''),
         created_at: @status_parser.created_at,
         edited_at: @status_parser.edited_at,
@@ -370,10 +370,6 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
     Formatter.instance.linkify([@status_parser.title.presence, @status_parser.spoiler_text.presence, @status_parser.url || @status_parser.uri].compact.join("\n\n"))
   end
 
-  def detected_language
-    LanguageDetector.instance.detect(@status_parser.text, @account) if supported_object_type?
-  end
-
   def unsupported_media_type?(mime_type)
     mime_type.present? && !MediaAttachment.supported_mime_types.include?(mime_type)
   end
diff --git a/app/lib/language_detector.rb b/app/lib/language_detector.rb
deleted file mode 100644
index 40452eddc..000000000
--- a/app/lib/language_detector.rb
+++ /dev/null
@@ -1,101 +0,0 @@
-# frozen_string_literal: true
-
-class LanguageDetector
-  include Singleton
-
-  WORDS_THRESHOLD        = 4
-  RELIABLE_CHARACTERS_RE = /[\p{Hebrew}\p{Arabic}\p{Syriac}\p{Thaana}\p{Nko}\p{Han}\p{Katakana}\p{Hiragana}\p{Hangul}\p{Thai}]+/m
-
-  def initialize
-    @identifier = CLD3::NNetLanguageIdentifier.new(1, 2048)
-  end
-
-  def detect(text, account)
-    input_text = prepare_text(text)
-
-    return if input_text.blank?
-
-    detect_language_code(input_text) || default_locale(account)
-  end
-
-  def language_names
-    @language_names = CLD3::TaskContextParams::LANGUAGE_NAMES.map { |name| iso6391(name.to_s).to_sym }.uniq
-  end
-
-  private
-
-  def prepare_text(text)
-    simplify_text(text).strip
-  end
-
-  def unreliable_input?(text)
-    !reliable_input?(text)
-  end
-
-  def reliable_input?(text)
-    sufficient_text_length?(text) || language_specific_character_set?(text)
-  end
-
-  def sufficient_text_length?(text)
-    text.split(/\s+/).size >= WORDS_THRESHOLD
-  end
-
-  def language_specific_character_set?(text)
-    words = text.scan(RELIABLE_CHARACTERS_RE)
-
-    if words.present?
-      words.reduce(0) { |acc, elem| acc + elem.size }.to_f / text.size > 0.3
-    else
-      false
-    end
-  end
-
-  def detect_language_code(text)
-    return if unreliable_input?(text)
-
-    result = @identifier.find_language(text)
-
-    iso6391(result.language.to_s).to_sym if result&.reliable?
-  end
-
-  def iso6391(bcp47)
-    iso639 = bcp47.split('-').first
-
-    # CLD3 returns grandfathered language code for Hebrew
-    return 'he' if iso639 == 'iw'
-
-    ISO_639.find(iso639).alpha2
-  end
-
-  def simplify_text(text)
-    new_text = remove_html(text)
-    new_text.gsub!(FetchLinkCardService::URL_PATTERN, '\1')
-    new_text.gsub!(Account::MENTION_RE, '')
-    new_text.gsub!(Tag::HASHTAG_RE) { |string| string.gsub(/[#_]/, '#' => '', '_' => ' ').gsub(/[a-z][A-Z]|[a-zA-Z][\d]/) { |s| s.insert(1, ' ') }.downcase }
-    new_text.gsub!(/:#{CustomEmoji::SHORTCODE_RE_FRAGMENT}:/, '')
-    new_text.gsub!(/\s+/, ' ')
-    new_text
-  end
-
-  def new_scrubber
-    scrubber = Rails::Html::PermitScrubber.new
-    scrubber.tags = %w(br p)
-    scrubber
-  end
-
-  def scrubber
-    @scrubber ||= new_scrubber
-  end
-
-  def remove_html(text)
-    text = Loofah.fragment(text).scrub!(scrubber).to_s
-    text.gsub!('<br>', "\n")
-    text.gsub!('</p><p>', "\n\n")
-    text.gsub!(/(^<p>|<\/p>$)/, '')
-    text
-  end
-
-  def default_locale(account)
-    account.user_locale&.to_sym || I18n.default_locale if account.local?
-  end
-end
diff --git a/app/lib/link_details_extractor.rb b/app/lib/link_details_extractor.rb
index d2bcf0c25..fabbd244d 100644
--- a/app/lib/link_details_extractor.rb
+++ b/app/lib/link_details_extractor.rb
@@ -2,6 +2,7 @@
 
 class LinkDetailsExtractor
   include ActionView::Helpers::TagHelper
+  include LanguagesHelper
 
   # Some publications wrap their JSON-LD data in their <script> tags
   # in commented-out CDATA blocks, they need to be removed before
@@ -218,14 +219,6 @@ class LinkDetailsExtractor
     nil
   end
 
-  def valid_locale_or_nil(str)
-    return nil if str.blank?
-
-    code,  = str.split(/_-/) # Strip out the region from e.g. en_US or ja-JA
-    locale = ISO_639.find(code)
-    locale&.alpha2
-  end
-
   def link_tag(name)
     document.xpath("//link[@rel=\"#{name}\"]").map { |link| link['href'] }.first
   end
diff --git a/app/models/user.rb b/app/models/user.rb
index bec94a1c8..a11bc3824 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -245,6 +245,10 @@ class User < ApplicationRecord
     save!
   end
 
+  def preferred_posting_language
+    settings.default_language || locale
+  end
+
   def setting_default_privacy
     settings.default_privacy || (account.locked? ? 'private' : 'public')
   end
diff --git a/app/services/activitypub/process_status_update_service.rb b/app/services/activitypub/process_status_update_service.rb
index 977928127..b1cea1cdf 100644
--- a/app/services/activitypub/process_status_update_service.rb
+++ b/app/services/activitypub/process_status_update_service.rb
@@ -120,7 +120,7 @@ class ActivityPub::ProcessStatusUpdateService < BaseService
     @status.text         = @status_parser.text || ''
     @status.spoiler_text = @status_parser.spoiler_text || ''
     @status.sensitive    = @account.sensitized? || @status_parser.sensitive || false
-    @status.language     = @status_parser.language || detected_language
+    @status.language     = @status_parser.language
     @status.edited_at    = @status_parser.edited_at || Time.now.utc if significant_changes?
 
     @status.save!
@@ -210,10 +210,6 @@ class ActivityPub::ProcessStatusUpdateService < BaseService
     { redis: Redis.current, key: "create:#{@uri}", autorelease: 15.minutes.seconds }
   end
 
-  def detected_language
-    LanguageDetector.instance.detect(@status_parser.text, @account)
-  end
-
   def create_previous_edit!
     # We only need to create a previous edit when no previous edits exist, e.g.
     # when the status has never been edited. For other cases, we always create
diff --git a/app/services/post_status_service.rb b/app/services/post_status_service.rb
index 294ae43eb..b3bc4a0a2 100644
--- a/app/services/post_status_service.rb
+++ b/app/services/post_status_service.rb
@@ -2,6 +2,7 @@
 
 class PostStatusService < BaseService
   include Redisable
+  include LanguagesHelper
 
   MIN_SCHEDULE_OFFSET = 5.minutes.freeze
 
@@ -109,10 +110,6 @@ class PostStatusService < BaseService
     raise Mastodon::ValidationError, I18n.t('media_attachments.validations.not_ready') if @media.any?(&:not_processed?)
   end
 
-  def language_from_option(str)
-    ISO_639.find(str)&.alpha2
-  end
-
   def process_mentions_service
     ProcessMentionsService.new
   end
@@ -165,7 +162,7 @@ class PostStatusService < BaseService
       sensitive: @sensitive,
       spoiler_text: @options[:spoiler_text] || '',
       visibility: @visibility,
-      language: language_from_option(@options[:language]) || @account.user&.setting_default_language&.presence || LanguageDetector.instance.detect(@text, @account),
+      language: valid_locale_or_nil(@options[:language].presence || @account.user&.preferred_posting_language || I18n.default_locale),
       application: @options[:application],
       rate_limit: @options[:with_rate_limit],
     }.compact
diff --git a/app/validators/import_validator.rb b/app/validators/import_validator.rb
index a182abfa5..9f19aee2a 100644
--- a/app/validators/import_validator.rb
+++ b/app/validators/import_validator.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'csv'
+
 class ImportValidator < ActiveModel::Validator
   KNOWN_HEADERS = [
     'Account address',
diff --git a/app/views/settings/preferences/other/show.html.haml b/app/views/settings/preferences/other/show.html.haml
index 539a70056..60e25fc2d 100644
--- a/app/views/settings/preferences/other/show.html.haml
+++ b/app/views/settings/preferences/other/show.html.haml
@@ -23,7 +23,7 @@
       = f.input :setting_default_privacy, collection: Status.selectable_visibilities, wrapper: :with_label, include_blank: false, label_method: lambda { |visibility| safe_join([I18n.t("statuses.visibilities.#{visibility}"), I18n.t("statuses.visibilities.#{visibility}_long")], ' - ') }, required: false, hint: false
 
     .fields-group.fields-row__column.fields-row__column-6
-      = f.input :setting_default_language, collection: [nil] + filterable_languages.sort, wrapper: :with_label, label_method: lambda { |locale| locale.nil? ? I18n.t('statuses.language_detection') : human_locale(locale) }, required: false, include_blank: false, hint: false
+      = f.input :setting_default_language, collection: [nil] + filterable_languages, wrapper: :with_label, label_method: lambda { |locale| locale.nil? ? I18n.t('statuses.default_language') : human_locale(locale) }, required: false, include_blank: false, hint: false
 
   .fields-group
     = f.input :setting_default_sensitive, as: :boolean, wrapper: :with_label
@@ -34,7 +34,7 @@
   %h4= t 'preferences.public_timelines'
 
   .fields-group
-    = f.input :chosen_languages, collection: filterable_languages.sort, wrapper: :with_block_label, include_blank: false, label_method: lambda { |locale| human_locale(locale) }, required: false, as: :check_boxes, collection_wrapper_tag: 'ul', item_wrapper_tag: 'li'
+    = f.input :chosen_languages, collection: filterable_languages, wrapper: :with_block_label, include_blank: false, label_method: lambda { |locale| human_locale(locale) }, required: false, as: :check_boxes, collection_wrapper_tag: 'ul', item_wrapper_tag: 'li'
 
   .actions
     = f.button :button, t('generic.save_changes'), type: :submit
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 85aa87c7a..600090e78 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -1307,13 +1307,13 @@ en:
         other: "%{count} videos"
     boosted_from_html: Boosted from %{acct_link}
     content_warning: 'Content warning: %{warning}'
+    default_language: Same as interface language
     disallowed_hashtags:
       one: 'contained a disallowed hashtag: %{tags}'
       other: 'contained the disallowed hashtags: %{tags}'
     edited_at: Edited %{date}
     errors:
       in_reply_not_found: The post you are trying to reply to does not appear to exist.
-    language_detection: Automatically detect language
     open_in_web: Open in web
     over_character_limit: character limit of %{max} exceeded
     pin_errors:
diff --git a/lib/tasks/repo.rake b/lib/tasks/repo.rake
index bbf7f20ee..795b54c59 100644
--- a/lib/tasks/repo.rake
+++ b/lib/tasks/repo.rake
@@ -96,7 +96,8 @@ namespace :repo do
     end.uniq.compact
 
     missing_available_locales = locales_in_files - I18n.available_locales
-    missing_locale_names = I18n.available_locales.reject { |locale| LanguagesHelper::HUMAN_LOCALES.key?(locale) }
+    supported_locale_codes    = Set.new(LanguagesHelper::SUPPORTED_LOCALES.keys + LanguagesHelper::REGIONAL_LOCALE_NAMES.keys)
+    missing_locale_names      = I18n.available_locales.reject { |locale| supported_locale_codes.include?(locale) }
 
     critical = false
 
@@ -123,7 +124,7 @@ namespace :repo do
 
     unless missing_locale_names.empty?
       puts pastel.yellow("You are missing human-readable names for these locales: #{pastel.bold(missing_locale_names.join(', '))}")
-      puts pastel.yellow("Add them to #{pastel.bold('HUMAN_LOCALES')} in app/helpers/settings_helper.rb or remove the locales from #{pastel.bold('I18n.available_locales')} in config/application.rb")
+      puts pastel.yellow("Add them to app/helpers/languages_helper.rb or remove the locales from #{pastel.bold('I18n.available_locales')} in config/application.rb")
     end
 
     if critical
diff --git a/spec/helpers/languages_helper_spec.rb b/spec/helpers/languages_helper_spec.rb
index 6db617824..b455cee33 100644
--- a/spec/helpers/languages_helper_spec.rb
+++ b/spec/helpers/languages_helper_spec.rb
@@ -3,9 +3,9 @@
 require 'rails_helper'
 
 describe LanguagesHelper do
-  describe 'the HUMAN_LOCALES constant' do
-    it 'includes all I18n locales' do
-      expect(described_class::HUMAN_LOCALES.keys).to include(*I18n.available_locales)
+  describe 'the SUPPORTED_LOCALES constant' do
+    it 'includes all i18n locales' do
+      expect(Set.new(described_class::SUPPORTED_LOCALES.keys + described_class::REGIONAL_LOCALE_NAMES.keys)).to include(*I18n.available_locales)
     end
   end
 
diff --git a/spec/lib/language_detector_spec.rb b/spec/lib/language_detector_spec.rb
deleted file mode 100644
index b7ba0f6c4..000000000
--- a/spec/lib/language_detector_spec.rb
+++ /dev/null
@@ -1,134 +0,0 @@
-# frozen_string_literal: true
-
-require 'rails_helper'
-
-describe LanguageDetector do
-  describe 'prepare_text' do
-    it 'returns unmodified string without special cases' do
-      string = 'just a regular string'
-      result = described_class.instance.send(:prepare_text, string)
-
-      expect(result).to eq string
-    end
-
-    it 'collapses spacing in strings' do
-      string = 'The formatting   in    this is very        odd'
-
-      result = described_class.instance.send(:prepare_text, string)
-      expect(result).to eq 'The formatting in this is very odd'
-    end
-
-    it 'strips usernames from strings before detection' do
-      string = '@username Yeah, very surreal...! also @friend'
-
-      result = described_class.instance.send(:prepare_text, string)
-      expect(result).to eq 'Yeah, very surreal...! also'
-    end
-
-    it 'strips URLs from strings before detection' do
-      string = 'Our website is https://example.com and also http://localhost.dev'
-
-      result = described_class.instance.send(:prepare_text, string)
-      expect(result).to eq 'Our website is and also'
-    end
-
-    it 'converts #hashtags back to normal text before detection' do
-      string = 'Hey look at all the #animals and #FishAndChips'
-
-      result = described_class.instance.send(:prepare_text, string)
-      expect(result).to eq 'Hey look at all the animals and fish and chips'
-    end
-  end
-
-  describe 'detect' do
-    let(:account_without_user_locale) { Fabricate(:user, locale: nil).account }
-    let(:account_remote) { Fabricate(:account, domain: 'joinmastodon.org') }
-
-    it 'detects english language for basic strings' do
-      strings = [
-        "Hello and welcome to mastodon how are you today?",
-        "I'd rather not!",
-        "a lot of people just want to feel righteous all the time and that's all that matters",
-      ]
-      strings.each do |string|
-        result = described_class.instance.detect(string, account_without_user_locale)
-
-        expect(result).to eq(:en), string
-      end
-    end
-
-    it 'detects spanish language' do
-      string = 'Obtener un Hola y bienvenidos a Mastodon. Obtener un Hola y bienvenidos a Mastodon. Obtener un Hola y bienvenidos a Mastodon. Obtener un Hola y bienvenidos a Mastodon'
-      result = described_class.instance.detect(string, account_without_user_locale)
-
-      expect(result).to eq :es
-    end
-
-    describe 'when language can\'t be detected' do
-      it 'uses nil when sent an empty document' do
-        result = described_class.instance.detect('', account_without_user_locale)
-        expect(result).to eq nil
-      end
-
-      describe 'because of a URL' do
-        it 'uses nil when sent just a URL' do
-          string = 'http://example.com/media/2kFTgOJLXhQf0g2nKB4'
-          cld_result = CLD3::NNetLanguageIdentifier.new(0, 2048).find_language(string)
-          expect(cld_result).not_to eq :en
-
-          result = described_class.instance.detect(string, account_without_user_locale)
-
-          expect(result).to eq nil
-        end
-      end
-
-      describe 'with an account' do
-        it 'uses the account locale when present' do
-          account = double(user_locale: 'fr')
-          result  = described_class.instance.detect('', account)
-
-          expect(result).to eq nil
-        end
-
-        it 'uses nil when account is present but has no locale' do
-          result = described_class.instance.detect('', account_without_user_locale)
-
-          expect(result).to eq nil
-        end
-      end
-
-      describe 'with an `en` default locale' do
-        it 'uses nil for undetectable string' do
-          result = described_class.instance.detect('', account_without_user_locale)
-
-          expect(result).to eq nil
-        end
-      end
-
-      describe 'remote user' do
-        it 'detects Korean language' do
-          string = '안녕하세요'
-          result = described_class.instance.detect(string, account_remote)
-
-          expect(result).to eq :ko
-        end
-      end
-
-      describe 'with a non-`en` default locale' do
-        around(:each) do |example|
-          before = I18n.default_locale
-          I18n.default_locale = :ja
-          example.run
-          I18n.default_locale = before
-        end
-
-        it 'uses nil for undetectable string' do
-          string = ''
-          result = described_class.instance.detect(string, account_without_user_locale)
-
-          expect(result).to eq nil
-        end
-      end
-    end
-  end
-end