Turkish localization presents severe problems for Sugar because Sugar is written in the Python programming language. In the Python programming language, case conversion is not locale-specific. This prevents correct handling of these characters: i, I, ı, İ. (the dot is treated much like a typical European accent, being neither added nor removed during case conversion)
Currently the Turkish locale settings make Sugar immediately crash. Even if this were fixed, Turkish text would still be mangled during case conversion.
There has been substantial discussion of this issue on the Unicode mailing list, and it is addressed in The Unicode Standard 5.0. PDFs of the relevant sections are at
Case conversion of Turkish is done routinely in several programming languages for which source code is available.