feat(i18n): Phase 1 — migrate 5 critical files from hardcoded text to i18n

47 new i18n keys added across all 13 locales (en, fr, es, de, pt, it,
nl, ru, ja, ko, zh, ar, fa). English and French are fully translated,
remaining locales use French as placeholder.

Files migrated:
- EditGlossaryDialog.tsx (18 strings)
- DeleteGlossaryDialog.tsx (7 strings)
- ProUpgradePrompt.tsx (10 strings)
- WebhookSnippet.tsx (4 strings)
- TranslationModeToggle.tsx (8 strings)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/app/dashboard/translate/TranslationModeToggle.tsx

@@ -9,6 +9,7 @@ import {
   TooltipTrigger,
 } from '@/components/ui/tooltip';
 import type { TranslationMode } from './types';
+import { useI18n } from '@/lib/i18n';
 
 interface TranslationModeToggleProps {
   mode: TranslationMode;
@@ -21,11 +22,12 @@ export function TranslationModeToggle({
   onModeChange,
   isPro,
 }: TranslationModeToggleProps) {
+  const { t } = useI18n();
   return (
     <TooltipProvider>
       <div className="flex flex-col gap-1.5">
         <label className="text-xs font-medium text-muted-foreground">
-          Translation Mode
+          {t('translate.mode.label')}
         </label>
         <div className="flex rounded-lg border border-border bg-muted p-1">
           <button
@@ -38,9 +40,9 @@ export function TranslationModeToggle({
             )}
             onClick={() => onModeChange('classic')}
           >
-            Classic
+            {t('translate.mode.classic')}
             <span className="ms-1.5 text-xs text-muted-foreground">
-              Fast
+              {t('translate.mode.classicDesc')}
             </span>
           </button>
           <Tooltip>
@@ -57,9 +59,9 @@ export function TranslationModeToggle({
                 onClick={() => isPro && onModeChange('llm')}
                 disabled={!isPro}
               >
-                Pro LLM
+                {t('translate.mode.proLlm')}
                 <span className="ms-1.5 text-xs text-muted-foreground">
-                  Context-Aware
+                  {t('translate.mode.proLlmDesc')}
                 </span>
                 {!isPro && (
                   <Lock className="absolute right-2 top-1/2 -translate-y-1/2 size-3 text-muted-foreground" />
@@ -68,7 +70,7 @@ export function TranslationModeToggle({
             </TooltipTrigger>
             {!isPro && (
               <TooltipContent side="top">
-                <p>Upgrade to Pro for LLM translation</p>
+                <p>{t('translate.mode.tooltip')}</p>
               </TooltipContent>
             )}
           </Tooltip>
@@ -76,9 +78,9 @@ export function TranslationModeToggle({
         {!isPro && (
           <p className="text-xs text-muted-foreground">
             <a href="/pricing" className="text-primary hover:underline">
-              Upgrade to Pro
+              {t('translate.mode.upgradeLink')}
             </a>{' '}
-            for LLM-powered translations
+            {t('translate.mode.upgradeDesc')}
           </p>
         )}
       </div>