[fix] don't show flags for languages without region identifier

SearXNG shows two different things:

region:
  "de-CH" is the equivalent of "Schweiz (de)" in DDG.

languages:
  "en" doesn't say anything about the location. It is up the engines to do their
  best to select English results without a region.

Suggested-by: @dalf https://github.com/searxng/searxng/pull/967#issuecomment-1072979693


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