not sure what exactly do you mean.
If you are trying to install software in different languages at the same time, then most likely you will always have a problem. If, for example the installer only speaks one language and your OS speaks another you will always have unreadable messages popping up.
If, on the other hand, you simply want to read a document or a website in another language then it works fine and you do not need to do anything. You might see Firefox showing question marks in its title bar, but that's as much trouble as you will see.