fix capitalization issues

gallery_dl/iso639_1.py

@@ -10,10 +10,11 @@
 
 def code_to_language(code, default="English"):
     """Map an ISO 639-1 language code to its actual name"""
-    return codes.get(code, default)
+    return codes.get(code.lower(), default)
 
 def language_to_code(lang, default="en"):
     """Map a language name to its ISO 639-1 code"""
+    lang = lang.capitalize()
     for code, language in codes.items():
         if language == lang:
             return code

test/test_iso639_1.py

@@ -14,10 +14,12 @@ class TestISO639_1(unittest.TestCase):
 
     def test_code_to_language(self):
         self.assertEqual(iso639_1.code_to_language("en"), "English")
+        self.assertEqual(iso639_1.code_to_language("FR"), "French")
         self.assertEqual(iso639_1.code_to_language("xx"), "English")
         self.assertEqual(iso639_1.code_to_language("xx", default=None), None)
     def test_language_to_code(self):
         self.assertEqual(iso639_1.language_to_code("English"), "en")
+        self.assertEqual(iso639_1.language_to_code("fRENch"), "fr")
         self.assertEqual(iso639_1.language_to_code("Nothing"), "en")
         self.assertEqual(iso639_1.language_to_code("Nothing", default=None), None)