[mod] replace engines_languages.json by engines_traits.json

Implementations of the *traits* of the engines.

Engine's traits are fetched from the origin engine and stored in a JSON file in
the *data folder*.  Most often traits are languages and region codes and their
mapping from SearXNG's representation to the representation in the origin search
engine.

To load traits from the persistence::

    searx.enginelib.traits.EngineTraitsMap.from_data()

For new traits new properties can be added to the class::

    searx.enginelib.traits.EngineTraits

.. hint::

   Implementation is downward compatible to the deprecated *supported_languages
   method* from the vintage implementation.

   The vintage code is tagged as *deprecated* an can be removed when all engines
   has been ported to the *traits method*.

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

searx/search/processors/abstract.py

@@ -138,7 +138,8 @@ class EngineProcessor(ABC):
         return False
 
     def get_params(self, search_query, engine_category):
-        """Returns a set of *request params* or ``None`` if request is not supported.
+        """Returns a set of (see :ref:`request params <engine request arguments>`) or
+        ``None`` if request is not supported.
 
         Not supported conditions (``None`` is returned):
 
@@ -159,11 +160,20 @@ class EngineProcessor(ABC):
         params['safesearch'] = search_query.safesearch
         params['time_range'] = search_query.time_range
         params['engine_data'] = search_query.engine_data.get(self.engine_name, {})
+        params['searxng_locale'] = search_query.lang
+
+        # deprecated / vintage --> use params['searxng_locale']
+        #
+        # Conditions related to engine's traits are implemented in engine.traits
+        # module. Don't do 'locale' decissions here in the abstract layer of the
+        # search processor, just pass the value from user's choice unchanged to
+        # the engine request.
 
         if hasattr(self.engine, 'language') and self.engine.language:
             params['language'] = self.engine.language
         else:
             params['language'] = search_query.lang
+
         return params
 
     @abstractmethod