Do you really mean "diacrytics" (which are just letters with additional glyph marks), or do you really mean all letters not typical ASCII a-z, A-Z, 0-9, punctuation, etc.
For example, should the following be accepted or rejected?
ø ß œ Ɣ
To do these types of comparisons, you can normalize the Unicode to a certain standard form (where diacritics are split to include the combining characters and then these are stripped) and some additional characters such as ß are force-converted to S. But more technically correct is to use a level 1 Unicode Collation Algorithm comparison. These are well beyond MC's capabilities.
Somewhere I have some code that does this - if you want it, and I can find it, it can be turned into a pscriptor scriplet so that you could perform this conversion and save the results to an MC field or two, or have it save a comparison result.