Arduino Leonardo keyboard
The Arduino Leonardo, in the same way as any keyboard, just sends keystroke data. It is down to your computer's operating system to translate those into individual letters and symbols. The Leonardo (and indeed any keyboard) has no say over how the operating system does that translation.

A brief google search (which led back to Stack Exchange) found me this project which may be of some interest. It allows you to automatically change the selected keyboard language depending on which keyboard is being used at any one moment in time.