Don't even get started on how to properly spell Yiddish words (or Hebrew or Russian or Arabic or Chinese, etc.) in English, since those languages aren't customarily written in the same alphabet as English.

I've seen "Bai Mir Bistu Schön," "Bei Mir Bist Du Shön," "Bay Mir Bist Du Schein," and probably a dozen other variations on that particular Yiddish song title. One's not really more "right" than another, since (I've been told) Yiddish traditionally was written in the Hebrew alphabet.