Why does the word "garage" have so many different pronunciations?

Whenever I'm teaching private students and we are faced with the word garage, I hesitate a little. Italians have borrowed the term garage, which they pronounce /gaˈraʒ/, to stand for the room/building where they keep their vehicles—also called a box in Italian.

In Italian the place where mechanics fix cars is not called a garage, but an officina. And to confuse my students further, in BrEng a garage [petrol station] is also the place where you can buy petrol/gas (AmEng gas station.)

I hesitate before pronouncing this word, because I know it has several different pronunciations:

1. /ˈɡærɑːʒ/
2. /ˈɡarɑː(d)ʒ/ (I think this pronunciation is very similar to the first)
3. /ˈɡærɪdʒ/

The first syllable is stressed whereas in the following the stress is on the second syllable

4. /gəˈräzh/ or /ɡəˈrɑːʒ/ and

5. /ɡəˈrɑrʒ/
   ^{(non-standard U.S. Midwest pronunciation)}

And I find myself pronouncing it in at least two ways, which befuddles the students (and makes me sound less credible!) I tell them that garage can be pronounced in more than one way but confess I don't know why. Personally, I blame it on the French :)

• Can someone explain why garage is pronounced in so many different ways?
• Which is the older pronunciation?

You are right, garage is a French loan and at first pronounced in the French way. After some time such words are pronounced in a way that is more conform to English pronunciation.

OALD has three pronunciations for BrE (stress on the first syllable), and two for AmE (stress on the second syllable). Normally the most common pronunciation is given first. So in BrE the French pronunciation is still the most frequent.

http://www.oxfordlearnersdictionaries.com/definition/english/garage_1?q=garage