[ticket/11542] Add unit tests for language_select()

PHPBB3-11542
[ticket/11542] Add lang_english_name to fixture

PHPBB3-11542
[ticket/11542] Add non-existing default value for language select

PHPBB3-11542
Merge remote-tracking branch 'nickvergessen/ticket/11542' into develop-olympus

* nickvergessen/ticket/11542:
  [ticket/11542] Add non-existing default value for language select
  [ticket/11542] Add lang_english_name to fixture
  [ticket/11542] Add unit tests for language_select()