Yes, adding another partition (your Files HDD) as secondary scratch drive will alleviate your current situation, if simply because you have an EXTREME shortage of available scratch disk space now.
But having no partitions whatsoever on the one and only drive in your laptop would be infinitely better.
Does this about summarize what you're running into Rounq?
If not, is it possible to provide additional info about the trouble?
Seems that the layers and groups showing up in the character panel's middle eastern features submenu would be an issue.
Is the problem that right-to-left typing works from one menu item, and not the other?
I notice that the setting seems to be type-layer specific, so if you have one set to right to left, another may be set to left to right.
Yes, this is a bug. The functionality isn't the same between the Type menu and the Character panel. I'm going to go ahead and log this bug.
Thanks for your feedback. If you have other bugs with Arabic, Hebrew, Farsi, or even Urdu, please let us know! 8-)