diff --git a/customize.dist/messages.js b/customize.dist/messages.js
index 06268dfd3..441ecf691 100755
--- a/customize.dist/messages.js
+++ b/customize.dist/messages.js
@@ -29,22 +29,66 @@ var map = {
     'sv': 'Svenska',
     //'te': 'తెలుగు',
     'uk': 'Українська',
-    'zh': '中文(簡體)',
+    'zh_Hans': '中文(簡體)',
+    'zh_Hant': '中文(正體)',
 };
 
 var Messages = {};
 var LS_LANG = "CRYPTPAD_LANG";
 var getStoredLanguage = function () { return localStorage && localStorage.getItem(LS_LANG); };
 var getBrowserLanguage = function () { return navigator.language || navigator.userLanguage || ''; };
+// 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-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();
+    return langAliases[lLower] || l;
+};
 var getLanguage = Messages._getLanguage = function () {
-    if (window.cryptpadLanguage) { return window.cryptpadLanguage; }
+    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;
+    }
     var l = getBrowserLanguage();
     try {
         l = getStoredLanguage() || getBrowserLanguage();
     } catch (e) { console.log(e); }
-    return map[l] ? l :
-            (map[l.split('-')[0]] ? l.split('-')[0] :
-                (map[l.split('_')[0]] ? l.split('_')[0] : 'en'));
+
+    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';
 };
 var language = getLanguage();
 window.cryptpadLanguage = language;
@@ -59,6 +103,8 @@ 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.js b/customize.dist/translations/messages.zh_Hans.js
similarity index 90%
rename from customize.dist/translations/messages.zh.js
rename to customize.dist/translations/messages.zh_Hans.js
index 1fe723a9b..9ff40d569 100644
--- a/customize.dist/translations/messages.zh.js
+++ b/customize.dist/translations/messages.zh_Hans.js
@@ -9,10 +9,9 @@
  * 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.js'], function (Messages) {
+define(['/common/translations/messages.zh_Hans.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 5cb823286..c030d3b28 100644
--- a/scripts/build.js
+++ b/scripts/build.js
@@ -51,6 +51,8 @@ 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 a6d71cbe2..71fe25e76 100644
--- a/src/worker/components/migrate-user-object.js
+++ b/src/worker/components/migrate-user-object.js
@@ -67,6 +67,8 @@ 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 141e25621..ce7da188e 100644
--- a/www/common/common-login.js
+++ b/www/common/common-login.js
@@ -262,7 +262,11 @@ define([
             if (!isRegister && !isProxyEmpty(rt.proxy)) {
                 var l = Util.find(rt.proxy, ['settings', 'general', 'language']);
                 var LS_LANG = "CRYPTPAD_LANG";
-                if (l) { localStorage.setItem(LS_LANG, l); }
+                if (l) {
+                    var langAliases = { 'zh': 'zh_Hans' };
+                    if (langAliases[l]) { l = langAliases[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.json b/www/common/translations/messages.zh_Hans.json
similarity index 100%
rename from www/common/translations/messages.zh.json
rename to www/common/translations/messages.zh_Hans.json
diff --git a/www/common/translations/messages.zh.json.license b/www/common/translations/messages.zh_Hans.json.license
similarity index 100%
rename from www/common/translations/messages.zh.json.license
rename to www/common/translations/messages.zh_Hans.json.license