These files have been generated from the existing XML files (cf.
fg-convert-translation-files in fgmeta).
Translations/en_US/FlightGear-nonQt.xlf is for a proper English
translation, where for instance "found %n airport(s)" would have two
plural forms, "found %n airport" and "found %n airports" (most
non-plural strings can be taken verbatim from the default translation,
and at this point there is no plural form at all yet).
