If you want to give your language experts a counter example, in German, the "sharp-S" / "eszet" letter "ß", compounded of "s" and "z", has no uppercase equivalent and is always written as "SS" when uppercased. For example straße ("street") becomes STRASSE. If you want to match case-insensitively here, you either have to normalize all ß to "ss" before comparing or you can "normalize" by converting to upper case.

But I admit that this is some corner case which is unlikely to affect non-Germans :-)