fix: add missing translations and fix namespace usage

- Fix srt-player to use srtT namespace for error messages
- Add deck_id.enterLanguageName and language labels (english, chinese, japanese, korean)
- Add memorize.review.nextCard translation
- Update all 8 locales with consistent translations

messages/de-DE.json

@@ -231,6 +231,7 @@
       "ease": "Schwierigkeit",
       "lapses": "Fehler",
       "showAnswer": "Antwort zeigen",
+      "nextCard": "Weiter",
       "again": "Nochmal",
       "hard": "Schwer",
       "good": "Gut",
@@ -626,6 +627,11 @@
     "sentencePlaceholder": "Satz eingeben",
     "wordPlaceholder": "Wort eingeben",
     "queryLang": "Abfragesprache",
+    "enterLanguageName": "Bitte Sprachnamen eingeben",
+    "english": "Englisch",
+    "chinese": "Chinesisch",
+    "japanese": "Japanisch",
+    "korean": "Koreanisch",
     "meanings": "Bedeutungen",
     "addMeaning": "Bedeutung hinzufügen",
     "partOfSpeech": "Wortart",