Switch language encoding (english/arabic/chinese) on-the-fly ?

I have a form with several input fields. Depending on the field the user gets in i want to switch the active language encoding to english, arabic or chinese (alignment and character set).

The appropriate character sets are enabled by the windows control center and i can do it manually, but for convenience for the user i want force it automatically by javascript logic.

I know that i can determine the active selected language by the navigator object, but it is read-only.

Does anybody know if this is possible and how to do it ?

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