QLocale toUpper/toLower don't call system alternative only icu

I want to change text to lower/upper case

Text is in Turkish :

Kullanım

if you look closer on i it don't have dot

but upper case variant

KULLANIM

In upper case variant that I is just standard ascii I

So when you want to properly convert text to lower case(from upper case) you will need to use QLocale("tr").toLower("KULLANIM").

But that don't work on Windows and MacOS I think

as base on this

https://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/text/qlocale.cpp#n3235

toLower/toUpper don't support non ICU variants

I can't use QString toUpper/toLower as it is working character by character so I can't use that.

So is it possible to add lower/upper system calls ?

I googled and windows 10 started to use ICU internaly and mac os use ICU so the results should be same 

ICU version is working fine.