I18N: Update po files for handler.c

I18N: Update po files for handler.c

Combine the old translations of the chopped strings

    s1 =
    "[-- This %s/%s attachment is not included, --]\n"

    s2 =
    "[-- and the indicated external source has --]\n"
    "[-- expired. --]\n"

into one translation for the single string

    s_new =
    "[-- This %s/%s attachment is not included, --]\n"
    "[-- and the indicated external source has --]\n"
    "[-- expired. --]\n"

Four translators (Galician (gl), Lithuanian (lt), Slovak (sk), Taiwanese
Mandarin (zh_WT)) seemed to have translated the old s2 as "s1 s2", so
the translation of s_new would have a doubling at the start. In these
versions we modified the translation to not have this doubling.