I don't know of the English "Ms." having an equivalent in other languages. Of course, I also don't know how to spell it out when not abbreviating it. "Miz"? That can't be right.
It doesn't have an unabbreviated form. It's always just "Ms." For that matter, "Mrs." is technically short for "Mistress"; "Missus" is just a vernacular rendering of how the abbreviation has come to be pronounced. It was originally a vulgar mispronunciation of the word, so it was spelled that way to convey dialect or vulgar speech in written fiction. But now "Mrs." has become a distinct title from "Mistress," so it's no longer considered an abbreviation. It's always just "Mrs." "Mister" is the only such title that still has a spelled-out form in modern English.