utf8CollateKey
Converts a string into a collation key that can be compared with other collation keys produced by the same function using strcmp().
The results of comparing the collation keys of two strings with strcmp() will always be the same as comparing the two original keys with g_utf8_collate().
Note that this function depends on the setlocale.
Return
a newly allocated string. This string should be freed with g_free() when you are done with it.
Parameters
str
a UTF-8 encoded string.
len
length of @str, in bytes, or -1 if @str is nul-terminated.