Make UI messages in _mplayer_patterns[] translatable

Summary:
i18n() does not work here because the kdelibs i18n system is not ready
yet at the time of static initialization of _mplayer_patterns[].

Test Plan: Tested by hand against Russian translation (kmplayer.mo).

Reviewers: vriezen, aacid

Reviewed By: aacid

Differential Revision: https://phabricator.kde.org/D4111