I haven't tested arabic fonts. There could be several reasons to fail though:
- in tab/window titles, there's no hope to have them displayed. MorphOS GUI doesn't support unicode, and arabic can't really be converted to classic charsets.

- in webview, if the text appears invisible, it's probably because arabic has to be rendered through a "complex rendering" method that is not implemented in cairo font backend. I might try to see what it looks like when disabled, but i fear it won't be too good (assuming it even works at all). Implementing the complex rendering mode implies switching to pango font backend, which could be possible, but i fear some speed penalties with it (and it also needs some work to get rid of gdk deps).