The font you use to add the text in Final Draft needs to be TrueType compatible, or when you'll paste text in Final Draft, the application will show you unknown characters.
This has also been mentioned on the official support page for Final Draft. I recommend you access the link to obtain additional information about supported and non-English languages.
Software Informer
Can we use Tamil language to write the script?
The font you use to add the text in Final Draft needs to be TrueType compatible, or when you'll paste text in Final Draft, the application will show you unknown characters.
This has also been mentioned on the official support page for Final Draft. I recommend you access the link to obtain additional information about supported and non-English languages.