[mod] fetch supported languages for several engines

utils/fetch_languages.py gets languages supported by each engine and
generates engines_languages.json with each engine's supported language.

tests/unit/engines/test_subtitleseeker.py

@@ -17,7 +17,7 @@ class TestSubtitleseekerEngine(SearxTestCase):
 
     def test_response(self):
         dicto = defaultdict(dict)
-        dicto['language'] = 'fr_FR'
+        dicto['language'] = 'fr-FR'
         response = mock.Mock(search_params=dicto)
 
         self.assertRaises(AttributeError, subtitleseeker.response, None)

tests/unit/engines/test_wikipedia.py

@@ -8,6 +8,8 @@ from searx.testing import SearxTestCase
 class TestWikipediaEngine(SearxTestCase):
 
     def test_request(self):
+        wikipedia.supported_languages = ['fr', 'en']
+
         query = 'test_query'
         dicto = defaultdict(dict)
         dicto['language'] = 'fr-FR'