The same problem exists for Arabic too, I think it is the general Right-To-Left languages support.
The editor can type Arabic but the cursor position is incorrect, also there is a problem when you try to highlight some Arabic text because the cursor does not point to the correct letters you want to highlight.
In one of my previous posts I informed you about this problem, which I think it is inherited from Delphi, (as I know, the PLSQL developper was built using Delphi) because Delphi editor suffuring the same thing, please check this with Borland if there is a new editor component that support RTL languages.
Regards.