[ticket/10521] Allow language switching by URL parameter

PHPBB3-10521
Merge remote-tracking branch 'github-vse/ticket/10521' into develop-ascraeus

* github-vse/ticket/10521:
  [ticket/10521] Allow language switching by URL parameter
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/10521] Allow language switching by URL parameter