diff --git a/customize.dist/messages.js b/customize.dist/messages.js
index 441ecf691..fd8a5f879 100755
--- a/customize.dist/messages.js
+++ b/customize.dist/messages.js
@@ -29,8 +29,8 @@ var map = {
     'sv': 'Svenska',
     //'te': 'తెలుగు',
     'uk': 'Українська',
-    'zh_Hans': '中文(簡體)',
-    'zh_Hant': '中文(正體)',
+    'zh': '中文(簡體)', // simplified
+    'zh_Hant': '中文(正體)', // traditional
 };
 
 var Messages = {};
@@ -40,55 +40,34 @@ var getBrowserLanguage = function () { return navigator.language || navigator.us
 // Normalize browser/localStorage language labels to CryptPad internal keys.
 // We keep this centralized to avoid scattered `if (l === 'zh') ...` logic.
 var langAliases = {
-    'zh': 'zh_Hans',
-    'zh-cn': 'zh_Hans',
-    'zh-sg': 'zh_Hans',
-    'zh-hans': 'zh_Hans',
-    'zh_hans': 'zh_Hans',
+    'zh-cn': 'zh',
+    'zh-sg': 'zh',
+    'zh-hans': 'zh',
 
     'zh-tw': 'zh_Hant',
     'zh-hk': 'zh_Hant',
     'zh-mo': 'zh_Hant',
     'zh-hant': 'zh_Hant',
-    'zh_hant': 'zh_Hant'
 };
 var normalizeLanguage = function (l) {
     if (!l) { return l; }
     // If it already matches a supported internal key, return as-is.
     if (map[l]) { return l; }
-    var lLower = String(l).toLowerCase();
+    var lLower = String(l).toLowerCase().replace('_', '-');
     return langAliases[lLower] || l;
 };
 var getLanguage = Messages._getLanguage = function () {
-    if (window.cryptpadLanguage) {
-        var original = window.cryptpadLanguage;
-        var normalized = normalizeLanguage(original);
-        // Migrate legacy localStorage language key.
-        if (original === 'zh' && normalized === 'zh_Hans') {
-            try { localStorage.setItem(LS_LANG, 'zh_Hans'); } catch (e) { console.log(e); }
-        }
-        window.cryptpadLanguage = normalized;
-        return normalized;
-    }
+    if (window.cryptpadLanguage) { return window.cryptpadLanguage; }
+
     var l = getBrowserLanguage();
     try {
         l = getStoredLanguage() || getBrowserLanguage();
     } catch (e) { console.log(e); }
-
-    var originalLang = l;
     l = normalizeLanguage(l);
-    // Migrate legacy localStorage language key.
-    if (originalLang === 'zh' && l === 'zh_Hans') {
-        try { localStorage.setItem(LS_LANG, 'zh_Hans'); } catch (e) { console.log(e); }
-    }
 
-    if (map[l]) { return l; }
-
-    var dash = (l || '').split('-')[0];
-    var under = (l || '').split('_')[0];
-    if (map[dash]) { return dash; }
-    if (map[under]) { return under; }
-    return 'en';
+    return map[l] ? l :
+            (map[l.split('-')[0]] ? l.split('-')[0] :
+                (map[l.split('_')[0]] ? l.split('_')[0] : 'en'));
 };
 var language = getLanguage();
 window.cryptpadLanguage = language;
@@ -103,8 +82,6 @@ var reqPaths = {
 Object.keys(map).forEach(function (k) {
     reqPaths["/common/translations/messages."+k+".js"] = "json!/common/translations/messages."+k+".json";
 });
-// Legacy locale key for Simplified Chinese (before zh_Hans)
-reqPaths["/common/translations/messages.zh.js"] = "json!/common/translations/messages.zh_Hans.json";
 require.config({
     map: {
         "*": reqPaths
diff --git a/customize.dist/translations/messages.zh_Hans.js b/customize.dist/translations/messages.zh.js
similarity index 90%
rename from customize.dist/translations/messages.zh_Hans.js
rename to customize.dist/translations/messages.zh.js
index 9ff40d569..1fe723a9b 100644
--- a/customize.dist/translations/messages.zh_Hans.js
+++ b/customize.dist/translations/messages.zh.js
@@ -9,9 +9,10 @@
  * If you want to check all the existing translation keys, you can open the internal language file
    but you should not change it directly (/common/translations/messages.{LANG}.js)
 */
-define(['/common/translations/messages.zh_Hans.js'], function (Messages) {
+define(['/common/translations/messages.zh.js'], function (Messages) {
     // Replace the existing keys in your copied file here:
     // Messages.button_newpad = "New Rich Text Document";
 
     return Messages;
 });
+
diff --git a/customize.dist/translations/messages.zh_Hant.js b/customize.dist/translations/messages.zh_Hant.js
new file mode 100644
index 000000000..9b67eba9d
--- /dev/null
+++ b/customize.dist/translations/messages.zh_Hant.js
@@ -0,0 +1,17 @@
+// SPDX-FileCopyrightText: 2026 XWiki CryptPad Team <contact@cryptpad.org> and contributors
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+/*
+ * You can override the translation text using this file.
+ * The recommended method is to make a copy of this file (/customize.dist/translations/messages.{LANG}.js)
+   in a 'customize' directory (/customize/translations/messages.{LANG}.js).
+ * If you want to check all the existing translation keys, you can open the internal language file
+   but you should not change it directly (/common/translations/messages.{LANG}.js)
+*/
+define(['/common/translations/messages.zh_Hant.js'], function (Messages) {
+    // Replace the existing keys in your copied file here:
+    // Messages.button_newpad = "New Rich Text Document";
+
+    return Messages;
+});
diff --git a/scripts/build.js b/scripts/build.js
index c030d3b28..5cb823286 100644
--- a/scripts/build.js
+++ b/scripts/build.js
@@ -51,8 +51,6 @@ try {
 }
 
 var preferredLanguage = config.preferredLanguage;
-var langAliases = { 'zh': 'zh_Hans' };
-if (langAliases[preferredLanguage]) { preferredLanguage = langAliases[preferredLanguage]; }
 var Preferred;
 
 var noScriptContent = [ Messages.ui_jsRequired ];
diff --git a/src/worker/components/migrate-user-object.js b/src/worker/components/migrate-user-object.js
index 71fe25e76..a6d71cbe2 100644
--- a/src/worker/components/migrate-user-object.js
+++ b/src/worker/components/migrate-user-object.js
@@ -67,8 +67,6 @@ const factory = (Feedback, Hash, Util,
             var migrateLanguage = function () {
                 if (!localStorage.CRYPTPAD_LANG) { return; }
                 var l = localStorage.CRYPTPAD_LANG;
-                var langAliases = { 'zh': 'zh_Hans' };
-                if (langAliases[l]) { l = langAliases[l]; }
                 userObject.settings.language = l;
             };
             if (version < 3) {
diff --git a/www/common/common-login.js b/www/common/common-login.js
index ce7da188e..141e25621 100644
--- a/www/common/common-login.js
+++ b/www/common/common-login.js
@@ -262,11 +262,7 @@ define([
             if (!isRegister && !isProxyEmpty(rt.proxy)) {
                 var l = Util.find(rt.proxy, ['settings', 'general', 'language']);
                 var LS_LANG = "CRYPTPAD_LANG";
-                if (l) {
-                    var langAliases = { 'zh': 'zh_Hans' };
-                    if (langAliases[l]) { l = langAliases[l]; }
-                    localStorage.setItem(LS_LANG, l);
-                }
+                if (l) { localStorage.setItem(LS_LANG, l); }
 
                 return void LocalStore.login(undefined, res.blockHash, res.uname, function () {
                     cb(void 0, res, RT);
diff --git a/www/common/translations/messages.zh_Hans.json b/www/common/translations/messages.zh.json
similarity index 100%
rename from www/common/translations/messages.zh_Hans.json
rename to www/common/translations/messages.zh.json
diff --git a/www/common/translations/messages.zh_Hans.json.license b/www/common/translations/messages.zh.json.license
similarity index 100%
rename from www/common/translations/messages.zh_Hans.json.license
rename to www/common/translations/messages.zh.json.license
diff --git a/www/common/translations/messages.zh_Hant.json.license b/www/common/translations/messages.zh_Hant.json.license
new file mode 100644
index 000000000..c487726db
--- /dev/null
+++ b/www/common/translations/messages.zh_Hant.json.license
@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2026 XWiki CryptPad Team <contact@cryptpad.org> and contributors
+
+SPDX-License-Identifier: AGPL-3.0-or-later