I posted this a while back, which might be helpful: Re^3: Removing Foreign Characters. There are other ways, of course, (I recall posting at least one other method myself), but that was the first one I found.

Update: Found a couple more... this one's also a bit old: Re: Diacritic-Insensitive and Case-Insensitve Sorting, and this one (the most recent) is my favorite: Re: fill diacritic into text. Have fun.

Another update: I realize I might be answering the wrong question -- and that's because there's some doubt about what your question really is. You say you're looking for

an easy way to make a regex pattern match ignore the accents on letters in other languages? For example, so that the word "café" and "cafe" would match (ie. ignore that the e's are actually different characters).

Um, so that "cafe" and "café" would match as opposed to what? The easiest way to make a regex ignore things is to use "." (e.g. /caf./ will match "cafe" and "café" and "cafè" and ... and caff and ...). How "exact" do you really need to be in your regex matching?

Are you really looking for a way to remove accents so you can do an exact match (eq or ne) to an unaccented string? (That's sort of what my various cited nodes are about.)