Rich,

... I've always been intrigued (?in this case means something like positively affected?) by the way non-native English speakers, even the most fluent ones, use idioms.

Yes, this is very nice the other way round too.

In American, I've always heard it as comparing apples and oranges. ... but I wouldn't be surprised to find that yours is a literal translation

Yes, we have "apples and pears" for comparing things, that you actually can't, because they are of a different kind. I guess apples and oranges does actually mean the same. It probably comes from times when we did not have oranges imported (too cold here), so we had to use the poor pear for that.

If idioms like this one are "in" your language, You (I) tend to use them without thinking that they might mean something totally different in the other language - or do not mean anything at all.

This can be even very harmful if it comes to cultural differences. I've heard of an AUDI-advertisement, where they had one of these before-after comparison things, showing a wreck on the left and the new AUDI-model on the righthandside. Unfortunately they published it in one of the arab countries where people read from right to left.

I've heard that the Mitsubishi Pajero was not sold too well in some spanish speaking countries first, until they found out that a pajero is a man who masturbates or something like that.

... I hope it's obvious that it isn't to comment on your knowledge of English

Even if it was, I would be thankful for that. I do not have as much possibilities to speak English/American as I'd like to. Reading, writing and getting corrected is the only way not to forget and to get better.

...That's the end of my trip down memory lane

I'm pleased You had a nice - 'though short - journey.