Sadly, the entire website itself is (obviously) in Chinese, so some inexperienced people may have hard time exploring the website. Anyway, here's a page about the Rukai source language (in English) from the official website of Taiwan Indigenous Culture Park. It has other pages for some other indigenous tribes as well.
Jika saya ada salah, mohon diperbaiki. If I am wrong, please correct me. (Native language)~ (Fluent second languages)~ (Understanding)~ (Learning/wanting to learn)~