Help F_ApiEnableUnicode(True) returns -1

With FM 12 and fdk 12 the F_ApiEnableUnicode(True)  returns -1. Help me pls.

The function is not working, with FM 10 I haven't this kind of problem. I tested the following code as described in fdkprogrammerguide.pdf and the result is incorrect, it displayed  the same characters both with Unicode disabled / enabled

F_ApiEnableUnicode(False);

F_ApiAlert("This is Unicode: \xC3\xA4 \xEB\xAE\xA4 \xD8\xB4",FF_ALERT_CONTINUE_NOTE);

F_ApiEnableUnicode(True);

F_ApiAlert("This is Unicode: \xC3\xA4 \xEB\xAE\xA4 \xD8\xB4",FF_ALERT_CONTINUE_NOTE);