[zokier]

From my point of view there could be one very simple solution: just add new codepoints in unicode for turkish I and i. So the latin i would follow the common case conventions, and turkish i would use whatever crazy stuff they have there.

Of course that might be bit late to do now, there is probably too much text encoded in the current format.

[mtts]

It's probably a bit late, agreed, but it seems to me this problem is just as much the fault of the encoding itself as it is the fault of PHP : Turkish i and I may look like Western European i and I but they're entirely different characters.