...as gm_Langpack_r_en_US was explicitly excluded from langs[] in
SelectLanguage, so addMatchingDictionaries was never called for it.  (This was
only evident in installation sets conaining only few langpacks, as the
"official" multi-lang installation set also contains en_GB etc., so appropriate
dictionaries were selected through those.)

Reworked the logic of chosing which langpacks to preselect (see the comment in
SelectLanguage); hope it still works as intended for the various cases (of which
the "official" multi-lang installation set is the only truly relevant one, for
now).

Change-Id: I31f531194c79e49c9c09e33454a7b0a82d9ff02f