If you want to match diacritics, then shouldn't you have the checkbox checked, not unchecked?
And yeah, regex is ascii until you specify one of the unicode flags.
I do have my own diacritics question, though, to ask of Mr. Void. Why do the default Filters have Match Diacritics checked, when it exists as a global option (Ctrl+M). Shouldn't the global option be respected, instead of being overridden by Filters, by default? Seems like a strange design, unless I'm just not understanding how diacritic matching works.