[mod] add 'Accept-Language' HTTP header to online processores

Most engines that support languages (and regions) use the Accept-Language from
the WEB browser to build a response that fits to the language (and region).

- add new engine option: send_accept_language_header

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

searx/engines/duckduckgo_definitions.py

@@ -27,6 +27,8 @@ about = {
     "results": 'JSON',
 }
 
+send_accept_language_header = True
+
 URL = 'https://api.duckduckgo.com/' + '?{query}&format=json&pretty=0&no_redirect=1&d=1'
 
 WIKIDATA_PREFIX = ['http://www.wikidata.org/entity/', 'https://www.wikidata.org/entity/']
@@ -62,7 +64,6 @@ def request(query, params):
     params['url'] = URL.format(query=urlencode({'q': query}))
     language = match_language(params['language'], supported_languages, language_aliases)
     language = language.split('-')[0]
-    params['headers']['Accept-Language'] = language
     return params