You could plausibly capitalize the ß into one of the homoglyphs for S. Then, lower() could detect the homoglyph and know how to lowercase it. This will have s

You could plausibly capitalize the ß into one of the homoglyphs for S. Then, lower() could detect the homoglyph and know how to lowercase it. This will have some side effects, though (e.g. a doubled lowercase version of your homoglyph will now not round-trip).