[mod] replace utils.match_language by locales.match_locale

This patch replaces the *full of magic* ``utils.match_language`` function by a
``locales.match_locale``.  The ``locales.match_locale`` function is based on the
``locales.build_engine_locales`` introduced in 9ae409a0 [1].

In the past SearXNG did only support a search by a language but not in a region.
This has been changed a long time ago and regions have been added to SearXNG
core but not to the engines.  The ``utils.match_language`` was the function to
handle the different aspects of language/regions in SearXNG core and the
supported *languages* in the engine.  The ``utils.match_language`` did it with
some magic and works good for most use cases but fails in some edge case.

To replace the concurrence of languages and regions in the SearXNG core the
``locales.build_engine_locales`` was introduced in 9ae409a0 [1].  With the last
patches all engines has been migrated to a ``fetch_traits`` and a
language/region concept that is based on ``locales.build_engine_locales``.

To summarize: there is no longer a need for the ``locales.match_language``.

[1] https://github.com/searxng/searxng/pull/1652



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