Most English people will pronounce a word ending in -a as "-er" - hence "Hiawath-er" or "Alabam-er". If a more open sound is required we'd expect it to be written "-ah"

There's not even consistency in how we mispronounce foreign names. Most English people pronounce Moscow as "Mosc-oh", whereas most Americans I've heard pronounce it "Mos-cow", to rhyme with the dairy animal.

I think the usages MthGM complained about in his original post have long died out - I was born in the '50s and I've never heard them pronounced other than "Mars-ay" and "Lee-on" - but with no pretence at a correct French accent of course.