Many OSX users reported their clients being in Japanese, rather than
English, since 0.9.0, which turned out to be due to
QSystemLocale::query for QSystemLocal::UILanguages (internally done by
Qt if a QLocale is passed to QTranslator::load) returning 'en', rather
than the proper local form (e.g. 'en-US').
As 'en' has no translation, the second language got picked up, which
happened to be 'ja', which does have a translation.
Fixes #1233 (but reintroduces #1194 on OSX)