Yes, not on purpose. As noted, there are many countries not listed too.
When 17.0.2 was in testing using grub, there were lots less languages too. But we can request that the languages be included. Perhaps it is just ‘what’s in the mind’ of the developers, which is understandable.
The good thing is that, even if any language is not in the install list, we can include it in the option, if it is in grub modules (which ‘ir’ is). You might find it interesting to note that Korean  is not in grub module and Mongolian is. Most linux developers are receptive to requests (except putting intel-ucode in kernel ); case in point, I (an insignificant user ) requested an ‘insignificant’ feature (halt) to the grub developers and it was done in a couple of days.
 To be fair, the grub developers had requested Korean users to help in translation for the modules. And I still wonder why f2fs is not in the grub capabilities (f2fs is a Korean innovation).
Ah, I talk too much. Cheers.