i18n("&Datei") surely looks ascii to me (although it doesn't really look like an English word, but that's another problem!).
Are you sure about the guilty line? Isn't there one with a special character, like an umlaut or something like that?
i18n() takes a UTF8 string, so if you want to put a special character (e.g. in someone's name, you have to use "recode l1..u8" to convert it to utf
.