Confirmation has arrived that rubai are, after all, an original form of poetry from Stoers, and not borrowed or some other form. A whole bunch of them here, in Srednestursky; The size varies in places and is not very similar to the classic one - apparently it has not yet been established. But without any doubt, this is exactly what can be considered the forerunner of the rubaiyat.
I do the poetic translation myself, so it turns out very poorly and not very quickly. I will post from time to time when I can. For now, I'll start with something a little ironic and very cute.
Nigūnsār wēnišn-it dušāgāh ma-rāy būd,
U xāmōš āwāz-it widandīg ma-rāy būd.
Ē, pad āhan tō hē az pad zan hamdamtar,
Be dōst rōštar az tō ne hagriz ma-rāy būd.
Your downcast, sad look always infuriates you,
I understand your muttering only sometimes.
Your love is true to iron - not to your wife;
But I have never had a brighter friend.