fix(captions): add language variant fallback + error on no files

Two fixes for captions downloads:

1. Language variant fallback: When user requests 'en' but the video only
   has 'en-GB' (or other regional variants), yt-dlp silently skips
   subtitle extraction because it uses exact language matching. Now the
   subtitleslangs list includes common regional variants (e.g. en-US,
   en-GB, en-AU, etc.) so yt-dlp can match the first available variant.

2. Error on no files: When yt-dlp completes successfully (ret=0) but
   produces no subtitle files (e.g. no matching language at all), the
   download was incorrectly shown as 'completed'. Now it's marked as
   'error' with a descriptive message like 'No subtitles found for
   language "en"'. Same treatment for thumbnail downloads.

app/dl_formats.py

@@ -10,6 +10,39 @@ CODEC_FILTER_MAP = {
     'vp9':  "[vcodec~='^vp0?9']",
 }
 
+# Common language variant suffixes that yt-dlp may encounter on YouTube and
+# other platforms.  When a user requests "en" we also try "en-GB", "en-US",
+# etc. so that a request isn't silently skipped when only a regional variant
+# exists.  yt-dlp processes the list in order and picks the first match.
+_LANGUAGE_REGION_VARIANTS = {
+    "en": ("US", "GB", "AU", "CA", "IN", "NZ", "IE", "ZA"),
+    "zh": ("CN", "TW", "HK", "SG"),
+    "pt": ("BR", "PT"),
+    "es": ("ES", "MX", "AR", "CO", "CL", "PE", "VE"),
+    "fr": ("FR", "CA", "BE", "CH"),
+    "de": ("DE", "AT", "CH"),
+    "ar": ("SA", "AE", "EG", "MA", "DZ"),
+    "nl": ("NL", "BE"),
+    "ro": ("RO", "MD"),
+    "ms": ("MY", "BN", "SG"),
+}
+
+
+def _subtitle_lang_list(language: str, include_orig: bool = False) -> list[str]:
+    """Build a prioritised list of subtitle language codes for yt-dlp.
+
+    Starts with the exact language, then appends common regional variants
+    (e.g. ``en`` → ``en-US, en-GB, en-AU, …``).  ``include_orig`` adds the
+    ``<lang>-orig`` tag that YouTube uses for original-language auto-captions.
+    """
+    langs = [language]
+    variants = _LANGUAGE_REGION_VARIANTS.get(language)
+    if variants:
+        langs.extend(f"{language}-{region}" for region in variants)
+    if include_orig:
+        langs.append(f"{language}-orig")
+    return langs
+
 
 def _normalize_caption_mode(mode: str) -> str:
     mode = (mode or "").strip()
@@ -141,21 +174,20 @@ def get_opts(
         if mode == "manual_only":
             opts["writesubtitles"] = True
             opts["writeautomaticsub"] = False
-            opts["subtitleslangs"] = [language]
+            opts["subtitleslangs"] = _subtitle_lang_list(language)
         elif mode == "auto_only":
             opts["writesubtitles"] = False
             opts["writeautomaticsub"] = True
-            # `-orig` captures common YouTube auto-sub tags. The plain language
+            opts["subtitleslangs"] = _subtitle_lang_list(language, include_orig=True)
-            # fallback keeps behavior useful across other extractors.
-            opts["subtitleslangs"] = [f"{language}-orig", language]
         elif mode == "prefer_auto":
             opts["writesubtitles"] = True
             opts["writeautomaticsub"] = True
-            opts["subtitleslangs"] = [f"{language}-orig", language]
+            opts["subtitleslangs"] = _subtitle_lang_list(language, include_orig=True)
         else:
+            # prefer_manual (default)
             opts["writesubtitles"] = True
             opts["writeautomaticsub"] = True
-            opts["subtitleslangs"] = [language, f"{language}-orig"]
+            opts["subtitleslangs"] = _subtitle_lang_list(language, include_orig=True)
 
     opts["postprocessors"] = postprocessors + (
         opts["postprocessors"] if "postprocessors" in opts else []

app/ytdl.py

@@ -704,6 +704,7 @@ class Download:
             status = await self.loop.run_in_executor(None, self.status_queue.get)
             if status is None:
                 log.info(f"Status update finished for: {self.info.title}")
+
                 return
             if self.paused:
                 self.info.status = 'paused'
@@ -775,6 +776,7 @@ class Download:
                     str(getattr(self.info, 'format', '')).lower() == 'txt'
                 ):
                     self.info.filename = rel_path
+                continue
 
             if 'thumbnail_file' in status:
                 thumbnail_file = status.get('thumbnail_file')
@@ -784,6 +786,11 @@ class Download:
                     self.info.size = os.path.getsize(thumbnail_file)
                 continue
 
+            # All remaining messages must have a 'status' key
+            if 'status' not in status:
+                log.warning(f"Skipping status update without 'status' key for {self.info.title}: {list(status.keys())}")
+                continue
+
             self.info.status = status['status']
             self.info.msg = status.get('msg')
             if 'download_phase' in status:
@@ -1006,6 +1013,33 @@ class DownloadQueue:
                 except OSError:
                     pass
             download.info.status = 'error'
+        else:
+            # Captions-only downloads that produced no subtitle files should be
+            # reported as an error rather than a silent "success".  This can
+            # happen when the requested language (e.g. "en") is unavailable and
+            # yt-dlp silently skips subtitle extraction without raising an
+            # error.
+            if getattr(download.info, 'download_type', '') == 'captions' and not download.info.filename:
+                subtitle_files = getattr(download.info, 'subtitle_files', [])
+                if not subtitle_files:
+                    log.warning(
+                        f"Captions download for \"{download.info.title}\" produced no files. "
+                        f"Requested language: {getattr(download.info, 'subtitle_language', 'en')}, "
+                        f"mode: {getattr(download.info, 'subtitle_mode', 'prefer_manual')}"
+                    )
+                    download.info.status = 'error'
+                    download.info.error = (
+                        f"No subtitles found for language \"{getattr(download.info, 'subtitle_language', 'en')}\". "
+                        f"The video may not have subtitles in the requested language."
+                    )
+            # Thumbnail-only downloads that produced no image file should also
+            # be reported as an error for the same reason.
+            elif getattr(download.info, 'download_type', '') == 'thumbnail' and not download.info.filename:
+                log.warning(
+                    f"Thumbnail download for \"{download.info.title}\" produced no file."
+                )
+                download.info.status = 'error'
+                download.info.error = "No thumbnail found for this video."
         download.close()
         if self.queue.exists(key):
             self.queue.delete(key)