In Turkish locale "i" character and "I" character is different. Therefore when you for example do:

"file".ToUpper();

It will output "FİLE" and not "FILE" in operating systems which using Turkish locale format for currency, time etc. So my operating system is actually English but because I'm using Turkish for region related settings, it using Turkish rules when converting string to uppercase.

So solution is to use:

"file".ToUpperInvariant();

That way it will output "FILE" correctly.

This issue exists for long time in SourceTree.