When you make converting Turkish chacter (i) with upper function, the result is (I). This is a problem. Because you want to pair two word but you can not pair with using the familiar functions which are upper, lower, initcap.
You can use NLS_UPPER function for the solution to solve this problem.
Example
SELECT NLS_UPPER(‘şampiyon’, ‘NLS_SORT = XTURKISH’) as Result FROM DUAL;
Result : ŞAMPİYON