In Options - Language Settings - Languages, in my case I select for Locale settings Hungarian (in hungarian the decimal point is: , coma), and I deselect Same as locale settings, in my document don't have effect. For decimal point I can't use . (point) only , (coma) I test it on ubuntu linux 11.10, windows 7 and xp, with english and hungarian locale settings (set in OS), with english and hungarian user interface, and in all case this option don't have effect. I suppose to change this checkbox to a list with comma and point, to change the preferred decimal point in my document.
This option defines only what character is inserted when you press the decimal separator key on the numeric keypad. It does not define the decimal separator for your locale. So closing as Not-A-Bug. Best regards. JBF