[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/google_images.py

@@ -43,6 +43,7 @@ max_page = 50
 """
 
 time_range_support = True
+language_support = True
 safesearch = True
 
 filter_mapping = {0: 'images', 1: 'active', 2: 'active'}