diff --git a/app/javascript/mastodon/features/compose/components/language_dropdown.jsx b/app/javascript/mastodon/features/compose/components/language_dropdown.jsx
index b164a07cbd..cb4662dfc9 100644
--- a/app/javascript/mastodon/features/compose/components/language_dropdown.jsx
+++ b/app/javascript/mastodon/features/compose/components/language_dropdown.jsx
@@ -238,6 +238,7 @@ class LanguageDropdown extends PureComponent {
   static propTypes = {
     value: PropTypes.string,
     frequentlyUsedLanguages: PropTypes.arrayOf(PropTypes.string),
+    guess: PropTypes.string,
     intl: PropTypes.object.isRequired,
     onChange: PropTypes.func,
   };
@@ -281,7 +282,7 @@ class LanguageDropdown extends PureComponent {
   };
 
   render () {
-    const { value, intl, frequentlyUsedLanguages } = this.props;
+    const { value, guess, intl, frequentlyUsedLanguages } = this.props;
     const { open, placement } = this.state;
     const current = preloadedLanguages.find(lang => lang[0] === value) ?? [];
 
@@ -294,7 +295,7 @@ class LanguageDropdown extends PureComponent {
           onClick={this.handleToggle}
           onMouseDown={this.handleMouseDown}
           onKeyDown={this.handleButtonKeyDown}
-          className={classNames('dropdown-button', { active: open })}
+          className={classNames('dropdown-button', { active: open, warning: guess !== '' && guess !== value })}
         >
           <Icon icon={TranslateIcon} />
           <span className='dropdown-button__label'>{current[2] ?? value}</span>
diff --git a/app/javascript/mastodon/features/compose/containers/language_dropdown_container.js b/app/javascript/mastodon/features/compose/containers/language_dropdown_container.js
index 64c90afa92..43907c7b49 100644
--- a/app/javascript/mastodon/features/compose/containers/language_dropdown_container.js
+++ b/app/javascript/mastodon/features/compose/containers/language_dropdown_container.js
@@ -2,6 +2,8 @@ import { createSelector } from '@reduxjs/toolkit';
 import { Map as ImmutableMap } from 'immutable';
 import { connect } from 'react-redux';
 
+import lande from 'lande';
+import { debounce } from 'lodash';
 
 import { changeComposeLanguage } from 'mastodon/actions/compose';
 
@@ -16,9 +18,80 @@ const getFrequentlyUsedLanguages = createSelector([
     .toArray()
 ));
 
+const ISO_639_MAP = {
+  afr: 'af', // Afrikaans
+  ara: 'ar', // Arabic
+  aze: 'az', // Azerbaijani
+  bel: 'be', // Belarusian
+  ben: 'bn', // Bengali
+  bul: 'bg', // Bulgarian
+  cat: 'ca', // Catalan
+  ces: 'cs', // Czech
+  ckb: 'ku', // Kurdish
+  cmn: 'zh', // Mandarin
+  dan: 'da', // Danish
+  deu: 'de', // German
+  ell: 'el', // Greek
+  eng: 'en', // English
+  est: 'et', // Estonian
+  eus: 'eu', // Basque
+  fin: 'fi', // Finnish
+  fra: 'fr', // French
+  hau: 'ha', // Hausa
+  heb: 'he', // Hebrew
+  hin: 'hi', // Hindi
+  hrv: 'hr', // Croatian
+  hun: 'hu', // Hungarian
+  hye: 'hy', // Armenian
+  ind: 'id', // Indonesian
+  isl: 'is', // Icelandic
+  ita: 'it', // Italian
+  jpn: 'ja', // Japanese
+  kat: 'ka', // Georgian
+  kaz: 'kk', // Kazakh
+  kor: 'ko', // Korean
+  lit: 'lt', // Lithuanian
+  mar: 'mr', // Marathi
+  mkd: 'mk', // Macedonian
+  nld: 'nl', // Dutch
+  nob: 'no', // Norwegian
+  pes: 'fa', // Persian
+  pol: 'pl', // Polish
+  por: 'pt', // Portuguese
+  ron: 'ro', // Romanian
+  run: 'rn', // Rundi
+  rus: 'ru', // Russian
+  slk: 'sk', // Slovak
+  spa: 'es', // Spanish
+  srp: 'sr', // Serbian
+  swe: 'sv', // Swedish
+  tgl: 'tl', // Tagalog
+  tur: 'tr', // Turkish
+  ukr: 'uk', // Ukrainian
+  vie: 'vi', // Vietnamese
+};
+
+const debouncedLande = debounce((text) => lande(text), 500, { trailing: true });
+
+const detectedLanguage = createSelector([
+  state => state.getIn(['compose', 'text']),
+], text => {
+  if (text.length > 20) {
+    const guesses = debouncedLande(text);
+    const [lang, confidence] = guesses[0];
+
+    if (confidence > 0.8) {
+      return ISO_639_MAP[lang];
+    }
+  }
+
+  return '';
+});
+
 const mapStateToProps = state => ({
   frequentlyUsedLanguages: getFrequentlyUsedLanguages(state),
   value: state.getIn(['compose', 'language']),
+  guess: detectedLanguage(state),
 });
 
 const mapDispatchToProps = dispatch => ({
diff --git a/app/javascript/styles/mastodon/components.scss b/app/javascript/styles/mastodon/components.scss
index 2c6efb71b4..ee1861ff5d 100644
--- a/app/javascript/styles/mastodon/components.scss
+++ b/app/javascript/styles/mastodon/components.scss
@@ -935,6 +935,16 @@ body > [data-popper-placement] {
     border-color: $ui-highlight-color;
     color: $primary-text-color;
   }
+
+  &.warning {
+    border-color: var(--goldenrod-2);
+    color: var(--goldenrod-2);
+
+    &.active {
+      background-color: var(--goldenrod-2);
+      color: var(--indigo-1);
+    }
+  }
 }
 
 .character-counter {
diff --git a/config/webpack/rules/babel.js b/config/webpack/rules/babel.js
index 902b823e1f..f1b53c3606 100644
--- a/config/webpack/rules/babel.js
+++ b/config/webpack/rules/babel.js
@@ -4,7 +4,7 @@ const { env, settings } = require('../configuration');
 
 // Those modules contain modern ES code that need to be transpiled for Webpack to process it
 const nodeModulesToProcess = [
-  '@reduxjs', 'fuzzysort'
+  '@reduxjs', 'fuzzysort', 'toygrad'
 ];
 
 module.exports = {
diff --git a/package.json b/package.json
index 4eb95d4389..d9c0e81601 100644
--- a/package.json
+++ b/package.json
@@ -82,6 +82,7 @@
     "imports-loader": "^1.2.0",
     "intl-messageformat": "^10.3.5",
     "js-yaml": "^4.1.0",
+    "lande": "^1.0.10",
     "lodash": "^4.17.21",
     "mark-loader": "^0.1.6",
     "marky": "^1.2.5",
diff --git a/yarn.lock b/yarn.lock
index 20d00347b8..f0d63c1ea9 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2930,6 +2930,7 @@ __metadata:
     jest: "npm:^29.5.0"
     jest-environment-jsdom: "npm:^29.5.0"
     js-yaml: "npm:^4.1.0"
+    lande: "npm:^1.0.10"
     lint-staged: "npm:^15.0.0"
     lodash: "npm:^4.17.21"
     mark-loader: "npm:^0.1.6"
@@ -11322,6 +11323,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"lande@npm:^1.0.10":
+  version: 1.0.10
+  resolution: "lande@npm:1.0.10"
+  dependencies:
+    toygrad: "npm:^2.6.0"
+  checksum: 10c0/27300be5937b6b9e245a7ea7a8216a0dcf5286a3b7ae38886c10c5c75b83fbfa1a69cd6754ab26bb38c6bd18aa8a2dcb62dea873506accb245cf82084acfee71
+  languageName: node
+  linkType: hard
+
 "language-subtag-registry@npm:^0.3.20":
   version: 0.3.22
   resolution: "language-subtag-registry@npm:0.3.22"
@@ -17127,6 +17137,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"toygrad@npm:^2.6.0":
+  version: 2.6.0
+  resolution: "toygrad@npm:2.6.0"
+  checksum: 10c0/96e42ced87431e99cec7d9b446c7827fe7782c2fd82bb5fc8c4a0855679011d809f9967096a60b4c8ceca867a29f1aadd62af447bdb652cb6f7fee279ae743ed
+  languageName: node
+  linkType: hard
+
 "tr46@npm:^1.0.1":
   version: 1.0.1
   resolution: "tr46@npm:1.0.1"