[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/boardreader.py

@@ -34,6 +34,7 @@ about = {
 categories = ["general", "social media"]
 paging = True
 time_range_support = True
+language_support = True
 
 base_url = "https://boardreader.com"
 time_range_map = {"day": "1", "week": "7", "month": "30", "year": "365"}