If so, then why other programmers are not putting language selector in their applications? Because we are following some guidelines*. And it's not that hard to install a new locale on your system(and make your friend happy ). It took me less than one minute(on Linux) to have my system in a complete new language. Why Firefox doesn't have a language selector (it have one for pages but not for UI), why Visual Studio doesn't have one? Because it's not normal to choose language for every application and adding language selection to an application just add complexity to user without any gain(maybe little). I'm against using language selectors in applications. An application should use system language.