Add Simplified Chinese Localization

Co-Authored-By: Ryan Cao <70191398+ryanccn@users.noreply.github.com>

frontend/src/features/system/components/LanguagePicker.tsx

@@ -18,6 +18,7 @@ export default function LanguagePicker() {
     pt_br: t('common:langBrPortuguese'),
     de: t('common:langGerman'),
     pl: t('common:langPolish'),
+    zh_cn: t('common:langSimplifiedChinese'),
   };
 
   const renderLanguagePicker = () => {