[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/__init__.py

@@ -44,6 +44,7 @@ ENGINE_DEFAULT_ARGS = {
     "enable_http": False,
     "using_tor_proxy": False,
     "display_error_messages": True,
+    "send_accept_language_header": False,
     "tokens": [],
     "about": {},
 }