I will address the original issue regarding '%z', but the second issue actually has to do with the Unicode representation of Turkish characters. In Turkish, the letter I ('\u0049') is a capital ı ('\u0131') and the letter İ ('\u0130') is a capital i ('\u0069'). In Python however, the lowercase of I is i, as in English.

>>> '\u0049'.lower()
'i'
>>> '\u0130'.lower()
'i̇'

We see that the lowercase forms of both I and İ are i, consistent with English in one case and Turkish in the other.