Well, umlauts do have an effect on the meaning of a German word in may cases, and the German s-zed is also useful - but an umlaut can be represented by an "e" after the vowel ("muede" instead of müde), and s-zed as "ss" ("muss" instead of muß).

Spanish tildes, as in niño, don't have a replacement, but I think they're more of a pronunciation guide - people know what to pronounce when they see "nino."

I can't comment on Irish words, except to say that the fadas give us fits in thread titles and in the Digital Tradition. I know some have tries to use slashes and spaces to replace fadas in Irish songs, but that doesn't seem to work very well, either.

-Joe Offer-