Comment by thaumasiotes

> If a language ships toUpper or a toLower function without a mandatory language field, it is badly designed too. The only slightly-better option is making toUpper and toLower ASCII-only and throwing error for any other character set.

There is a deeper bug within Unicode.

The Turkish letter TURKISH CAPITAL LETTER DOTLESS I is represented as the code point U+0049, which is named LATIN CAPITAL LETTER I.

The Greek letter GREEK CAPITAL LETTER IOTA is represented as the code point U+0399, named... GREEK CAPITAL LETTER IOTA.

The relationship between the Greek letter I and the Roman letter I is identical in every way to the relationship between the Turkish letter dotless I and the Roman letter I. (Heck, the lowercase form is also dotless.) But lowercasing works on GREEK CAPITAL LETTER IOTA because it has a code point to call its own.

Should iota have its own code point? The answer to that question is "no": it is, by definition, drawn identically to the ascii I. But Unicode has never followed its principles. This crops up again and again and again, everywhere you look. (And, in "defense" of Unicode, it has several principles that directly contradict each other.)

Then people come to rely on behavior that only applies to certain buggy parts of Unicode, and get messed up by parts that don't share those particular bugs.