i18n: add French, Russian, Chinese Simplified, and Dutch translations

client/src/i18n/TranslationContext.tsx

@@ -3,18 +3,22 @@ import { useSettingsStore } from '../store/settingsStore'
 import de from './translations/de'
 import en from './translations/en'
 import es from './translations/es'
+import fr from './translations/fr'
+import ru from './translations/ru'
+import zh from './translations/zh'
+import nl from './translations/nl'
 
 type TranslationStrings = Record<string, string>
 
-const translations: Record<string, TranslationStrings> = { de, en, es }
+const translations: Record<string, TranslationStrings> = { de, en, es, fr, ru, zh, nl }
-const LOCALES: Record<string, string> = { de: 'de-DE', en: 'en-US', es: 'es-ES' }
+const LOCALES: Record<string, string> = { de: 'de-DE', en: 'en-US', es: 'es-ES', fr: 'fr-FR', ru: 'ru-RU', zh: 'zh-CN', nl: 'nl-NL' }
 
 export function getLocaleForLanguage(language: string): string {
   return LOCALES[language] || LOCALES.en
 }
 
 export function getIntlLanguage(language: string): string {
-  return language === 'de' || language === 'es' ? language : 'en'
+  return ['de', 'es', 'fr', 'ru', 'zh', 'nl'].includes(language) ? language : 'en'
 }
 
 interface TranslationContextValue {

client/src/pages/SettingsPage.tsx

@@ -270,6 +270,10 @@ export default function SettingsPage(): React.ReactElement {
                   { value: 'de', label: 'Deutsch' },
                   { value: 'en', label: 'English' },
                   { value: 'es', label: 'Español' },
+                  { value: 'fr', label: 'Français' },
+                  { value: 'nl', label: 'Nederlands' },
+                  { value: 'ru', label: 'Русский' },
+                  { value: 'zh', label: '中文' },
                 ].map(opt => (
                   <button
                     key={opt.value}