add configurable locale for metadata

dlibrary/dlibrary.py

@@ -61,7 +61,7 @@ async def fetch_async(args):
     thumbnails_dir = args.destdir / 'site' / 'thumbnails'
     thumbnails_dir.mkdir(parents=True, exist_ok=True)
 
-    async with DlsiteAPI() as api:
+    async with DlsiteAPI(locale=args.locale) as api:
         for work_path in (args.destdir / 'extract').iterdir():
             work_id = work_path.name
 
@@ -459,6 +459,14 @@ parser_extract.add_argument(
 parser_extract.set_defaults(func=extract)
 
 parser_fetch = subparsers.add_parser('fetch', help='fetch metadata and thumbnails')
+parser_fetch.add_argument(
+    '-l', '--locale',
+    type=str,
+    default=getenv('DLIBRARY_LOCALE', 'en_US'),
+    help=('locale to use when requesting metadata (e.g. "ja_JP", "en_US"). '
+          'May still fall back to Japanese if metadata in other languages is unavailable. '
+          '(default: $DLIBRARY_LOCALE or en_US)'),
+)
 parser_fetch.set_defaults(func=fetch)
 
 parser_collate = subparsers.add_parser(