Going back to the original question, when I was a choirboy (sort of) we had a few performances in which a Latin version of a hymn was sung as a "counter" by a solo voice while the main choir sang the English.

This didn't happen very often, but the "countermelody" was generally just something very close to the alto harmony, with the minor adjustments needed for differences in syllables. (The strong singers we had were mostly female voices, but the melody usually is in the sopranos so the alto might be prefered regardless?)

Depending on the background of the congregation, the same sort of thing could probably be done with any other language. I would have expected that perhaps a German version would have "sounded right" for many of the people in churches in my area, but I've heard a few quite lovely Swedish and Dutch renditions of well known hymns that probably would have fit well as counterpoint to English with very little "arrangement."

John