I can start by directly saying that some languages you will NOT find, but most LTR (left to right) using roman letters will work. RTL (right to left) and languages that uses non-roman letters are at times a bit trickier.
The keyboard way
This will “just” give you a keyboard and wordbook in the language needed, and is often the easy to fix it.
Stock HTC Sense input
Keyboard got around 40 different languages in it, including Arabic and Hebrew, at least it does on my Swedish One. You see just what languages you have in Settings > Language & keyboard > HTC Sense input > Keyboard selection, where you select the keyboards you want to use.
This you download from play store, it’s however not available for all regions. In this you have around 57 different languages to use. With it installed and active, you go to Settings > Languages & keyboard > Google keyboard > Input language, where you have a list of the available languages.
One of the most known 3rd party keyboards with around 58 different languages in it (download from play, there’s a trail version as well), which have a bit more support for non-roman/latin languages then both htc sense input and google keyboard.
Other 3rd party keyboards
There is of course more keyboards that can do this, but I’ve covered the most common/best/what I prefer.
The system language way
This is the more tricker way since in 4.2.2 the way locale (system language and so) was set changed, but this will give you a full Swedish phone on the One you got from Germany that don’t have Swedish as system language. Works for most roman/latin based languages, can be a little tricky for RTL languages or non-roman/latin letter based languages.
I have written a guide for this HERE if you need it.