I'm trying to add an Arabic subtitle in DVDSP3. I create a new subtitle (in the subtitle stream), I change the Keyboard input to Arabic... The moment I try to type something (in the Inspector window), the keyboard changes back to default English.
Any idea why?

Disclaimer: I don't know much about Mac's or FCP

However, I do know how such things are supposed to work in the Windows
world. You need to have the language installed with the aproriate fonts.

If those are missing you cannot write or read such languages.

Are you sure both options are installed? Can you write it in other applications
like a word processor? What happens if you copy & paste it from there into
FCP?

I'm afraid that is the best I can do. Hopefully other people have some more
answers for you. If not I suggest you try the Apple forums!

well, language is installed, and I can type in other applications.

Anyways, I tried typing Arabic in Text editor, then Copy/Paste in DVDSP3. It worked! I guess I have to live with it like that for now.

Glad you found a work-around! Perhaps that's a bug in DVDSP. I would suggest
you mention it to Apple, hopefully it can be fixed in a later version.