[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/wikidata.py

@@ -40,6 +40,7 @@ about = {
     "require_api_key": False,
     "results": 'JSON',
 }
+language_support = True
 
 display_type = ["infobox"]
 """A list of display types composed from ``infobox`` and ``list``.  The latter