Apple – Press Info – Mac OS X Hits Stores This Weekend (2001) listed seven languages for 10.0. From an archived Apple knowledge base article Mac OS X 10.6: Changing the direction of text I know that Snow Leopard included support for right-to-left and bidirectional text. From the knowledge base:
… When using certain right-to-left writing systems such as Arabic, Hebrew, Yiddish, Persian, Pashto, and Urdu, you may need to quote words from left-to-right writing systems, such as English. When right-to-left text is mixed with left-to-right text, it is called bidirectional text. …
- I can't tell which version of the operating system introduced support for RTL.
Apple - Mac OS X Snow Leopard - Technical specifications doesn't list Arabic or Hebrew amongst the languages, so (by implication) whilst operating system localisations at that time did not include those languages, the OS did support RTL.
Another archived article, Hebrew & Arabic Language Kit: System Direction Issues, reminds me that for less recent versions of the OS, Apple's installer offered language kits (more recent installers include those languages by default).
I tried searching domains such as mellel.com, redlers.com and www.apple.com/pr – e.g. https://duckduckgo.com/?q=languages%20%22Mac%20OS%20X%22%20site:www.apple.com/pr/ – couldn't find an answer.
If it helps: https://en.wikipedia.org/wiki/Mellel states that development of Mellel began in 2002 (and I recall Mellel being renowned for RTL support).