MessageDlg(msgSameSignExplain, mtError, [mbNo, mbYes], 0);
A caption and buttons are still English, that's naturally.
...but there are incorrect chars if the same string in siLang.MessageDlg
siLang.MessageDlg(msgSameSignExplain, mtError, [mbNo, mbYes], 0);
A caption and buttons are Turkish per siLang component settings.

There are obviously different messages fonts.
Is there any way to control siLang.MessageDlg() font properties?