All engines has been migrated from ``supported_languages`` to the
``fetch_traits`` concept. There is no longer a need for the obsolete code that
implements the ``supported_languages`` concept.
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
The language_support variable is set to True by default,
and set to False in only 5 engines.
Except the documentation and the /config URL, this variable is not used.
This commit remove the variable definition in the engines, and
set value according to supported_languages length: False when the length is 0,
True otherwise.
Close#2485
Searching for english is now giving all pages results.
Instead searching for a specific language different from english
is correctly returning only translated pages for the selected language.
