[fix] set language_support for engines with languages in traits (#6258)

In the past, the engine option ``language_support`` was not consistently
maintained; with this patch, a ValueError is now thrown if an engine has
languages in its traits but language_support is not set to True.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/dailymotion.py

@@ -40,6 +40,7 @@ categories = ["videos"]
 paging = True
 page_size = 10
 
+language_support = True
 time_range_support = True
 time_delta_dict = {
     "day": timedelta(days=1),