Add concurrent connections i18n keys

Add new i18n keys "concurrent_fragments" and "concurrent_fragments_help" to multiple language JSON files (ar, de, en, es, fr, hi, id, it, ja, pl, pt, ru, tr, zh). These expose a UI option for the number of concurrent connections per download with a help string (default: 1, warns about throttling/temporary blocks). Strings were added in English across locales and may need translation.

ytsage/languages/fr.json

@@ -342,7 +342,9 @@
     "filename_format_help": "Variables disponibles : %(title)s, %(uploader)s, %(upload_date)s, %(resolution)s, %(id)s, %(ext)s. La syntaxe standard des modèles de sortie yt-dlp est prise en charge.",
     "tab_general": "Général",
     "tab_format": "Format",
-    "tab_file": "Fichier"
+    "tab_file": "Fichier",
+    "concurrent_fragments": "Concurrent Connections",
+    "concurrent_fragments_help": "Number of connections per download. Higher values bypass throttling but may cause temporary blocks if set too high. Default: 1."
   },
   "main_ui": {
     "url_placeholder": "Entrer l'URL de la vidéo ou de la playlist YouTube",
@@ -624,4 +626,4 @@
     "update_failed": "❌ Échec de la mise à jour : {error}",
     "check_failed": "Échec de la vérification des mises à jour. Veuillez vérifier votre connexion Internet."
   }
-}
+}