Add localization for status and error messages

Replaced hardcoded status and error messages with localized strings throughout the downloader, main GUI, update dialog, and video info components. Updated English and Spanish language files with new keys for download statuses, errors, playlist info, and UI labels to improve internationalization and maintainability.

languages/en.json

@@ -154,6 +154,22 @@
 
   "download": {
     "preparing": "Preparing download...",
+    "starting": "🚀 Starting download...",
+    "fetching_info": "🔍 Fetching video information...",
+    "preparing_streams": "🎯 Preparing video streams...",
+    "downloading_audio": "⏬ Downloading audio...",
+    "downloading_video": "⏬ Downloading video...",
+    "downloading_subtitle": "⏬ Downloading subtitle...",
+    "downloading": "⏬ Downloading...",
+    "completed": "✅ Download completed!",
+    "video_completed": "✅ Video download completed!",
+    "audio_completed": "✅ Audio download completed!",
+    "subtitle_completed": "✅ Subtitle download completed!",
+    "completed_cleaning": "✅ Download completed! Cleaning up...",
+    "cancelled": "Download cancelled",
+    "processing_playlist": "📋 Processing playlist data...",
+    "paused": "Download paused",
+    "resumed": "Download resumed",
     "please_enter_url": "Please enter a URL first.",
     "please_set_path": "Please set a download path first.",
     "please_enter_url_and_path": "Please enter a URL and set download path.",
@@ -164,6 +180,7 @@
     "checking": "Checking for updates...",
     "update_available": "Update available!\nCurrent version: {current}\nLatest version: {latest}",
     "up_to_date": "yt-dlp is up to date (version {version})",
+    "already_up_to_date": "✅ yt-dlp is already up to date!",
     "could_not_determine": "Could not determine versions.",
     "error_comparing": "Error comparing versions: {error}",
     "update_available_failed": "Update available! (Comparison failed)\nCurrent: {current}\nLatest: {latest}",
@@ -329,6 +346,34 @@
   "status": {
     "ready": "Ready",
     "file_exists": "⚠️ File already exists",
+    "video_file_exists": "⚠️ Video file already exists",
+    "audio_file_exists": "⚠️ Audio file already exists", 
+    "subtitle_file_exists": "⚠️ Subtitle file already exists",
     "cancelling": "Cancelling download..."
+  },
+  "errors": {
+    "playlist_no_videos": "Error: Playlist contains no valid videos.",
+    "playlist_no_url": "Error: Could not get URL for the first playlist video.",
+    "ytdlp_not_found": "Error: yt-dlp executable not found. Please install yt-dlp first.",
+    "ytdlp_not_found_path": "Error: yt-dlp executable not found. This could be due to improper installation or a PATH issue.",
+    "no_data_returned": "Error: No data returned from yt-dlp",
+    "no_format_info": "Error: No format information available.",
+    "analysis_timeout": "Error: Analysis timed out. Please try again.",
+    "invalid_speed_limit": "❌ Error: Invalid speed limit value set in settings.",
+    "ytdlp_failed": "Error: yt-dlp failed: {error}",
+    "parse_failed": "Error: Failed to parse yt-dlp output: {error}",
+    "analysis_failed": "Error: Analysis failed: {error}",
+    "generic_error": "Error: {error}"
+  },
+  "update_dialog": {
+    "title": "Update Available"
+  },
+  "playlist": {
+    "unknown": "Unknown Playlist",
+    "total_videos": "Total Videos: {count}",
+    "display_format": "Playlist: {title} | {count} videos"
+  },
+  "subtitle_selection": {
+    "count_selected": "{count} selected"
   }
 }