search: make language configurable from settings.yml

searx/preferences.py

         super(Preferences, self).__init__()
 
         self.key_value_settings = {'categories': MultipleChoiceSetting(['general'], choices=categories),
-                                   'language': EnumStringSetting('all', choices=LANGUAGE_CODES),
+                                   'language': EnumStringSetting(settings['search']['language'],
+                                                                 choices=LANGUAGE_CODES),
                                    'locale': EnumStringSetting(settings['ui']['default_locale'],
                                                                choices=settings['locales'].keys() + ['']),
                                    'autocomplete': EnumStringSetting(settings['search']['autocomplete'],

searx/settings.yml

 search:
     safe_search : 0 # Filter results. 0: None, 1: Moderate, 2: Strict
     autocomplete : "" # Existing autocomplete backends: "dbpedia", "duckduckgo", "google", "startpage", "wikipedia" - leave blank to turn it off by default
+    language : "all"
 
 server:
     port : 8888

searx/settings_robot.yml

 search:
     safe_search : 0
     autocomplete : ""
+    language: "all"
 
 server:
     port : 11111