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.

src/gui/ytsage_gui_video_info.py

@@ -218,10 +218,10 @@ class VideoInfoMixin:
 
         if hasattr(self, "is_playlist") and self.is_playlist:
             # Playlist Mode: Show playlist title and video count
-            self.title_label.setText(self.playlist_info.get("title", "Unknown Playlist"))
+            self.title_label.setText(self.playlist_info.get("title", _("playlist.unknown")))
 
             num_videos = len(getattr(self, "playlist_entries", []))
-            self.duration_label.setText(f"Total Videos: {num_videos}")
+            self.duration_label.setText(_("playlist.total_videos", count=num_videos))
 
             # Hide video-specific info
             self.channel_label.setText("")
@@ -295,7 +295,7 @@ class VideoInfoMixin:
             logger.info(f"Selected subtitles: {self.selected_subtitles}")
             # Update UI to reflect selection
             count = len(self.selected_subtitles)
-            self.selected_subs_label.setText(f"{count} selected")
+            self.selected_subs_label.setText(_("subtitle_selection.count_selected", count=count))
             self.subtitle_select_btn.setProperty("subtitlesSelected", count > 0)
 
             # Enable/disable the merge checkbox in the parent window