This reverts commit edd2290d71. For the reasons of this reverting, see the thread at <https://sourceforge.net/p/flightgear/mailman/flightgear-devel/thread/CAHtsj_eFdxLoXXoNq%3D3OKNRmyR6-FowFL97TASdQJx8N05Lmig%40mail.gmail.com/#msg35580548>, including <https://sourceforge.net/p/flightgear/mailman/message/35584363/>, <https://sourceforge.net/p/flightgear/mailman/message/35584803/> and <https://sourceforge.net/p/flightgear/mailman/message/35585421/> (appearing out-of-thread according to the SF mailing list archive...).
edd2290d71
Also remove <intl include="Translations/locale.xml"/> from preferences.xml. Something equivalent based on readProperties() is done in FlightGear (cf. FGLocale::FGLocale() in flightgear/src/Main/locale.cxx).
Separate options and menu translations. Use subdirectories with individual resources for each language.