Imperial Russia, 1890:
Armenians
Azeri Turks
Bashkirs
Belarussians
Chechens
Estonians
Finns
Georgians
Germans (Baltic, Volga)
Greeks
Inuit
Jews (Yiddish)
Kalmucks
Karelians
Kazakhs
Kirghiz
Krim Tatars
Lapps
Latvians
Lithuanians
Moldovans (Romanians)
Mongols
Mordvins
Ossetians
Poles
Russians
Samoyeds
Swedes
Tajiks
Turkmens
Ukranians
Uzbeks
Volga Tatars
That's 33. How many more do you want?
Dammit, I wanted to point this out.
You forgot the Mountain Jews. Seriously. Mountain Jews.
But in any case, the multiethnic nature of both the Russian Empire and the Mongolian Empires is rather...an oddity. Neither were known for...tolerance and were rather in fact infamous for shall we say...inspired methods of rule. Both were known for and did commit brutal acts of mass murder and forced migration but in the end, both came to rule over a truly vast and diverse subject people. The Mongols because reputation often preced them, thus lessening desire for overt resistance in many cases and because the Mongols never engaged in specific ethno exterminations.
The Russian Czars were a bit less extreme in the initial conquest but there line of continuity lasted and gave a gruesome counter example of a multicultural empire, possibly even multicultural society. It allowed them to exist and continue existing. Sounds kinda obvious but the important bit is is that unlike current history where in certain, more elderly minded, modernization and westernization are thought to be synonymous. But in the former Russian Empire, whole nations and ethnicities were able to hold on to there identities, in spite of the brutality of the Czars.
Although the fact that outside of revolt, or recruitment, the Russian Empire could be comparitively light handed in day to day affairs.
Modern day Multiculturalism is both a revolution in thought as much as a reaction to the extremes of Western Imperialism and Nazism.
Russian Imperialism was slightly different. Kiss the boot and they would take it off your throat. And give you a kick in the bum just for reminding. Other than that, you were left alone.
They never expected you to like the boot and sing praises to the cobbler who made it.
But yeah, if you would define multicultural/multiethnic as similar, then take the Russian Empire and go with it. Like...instead of displacing Native American, assimilate there nations as States of the Union and keepbto decent treaties.
That always was a sticking point for me. The trashing of treaties. The slaughters and brutal massacres are one thing, but the sheer dishonorable doucheiness of constantly going back on treaties....
Mind you, even going the nicer manner, there isnt an honestly decent and noble way to do almost anything of note as far as nationbuilding in those days. Russian Style is about the nicest.
As in, you get to exist and not be turned into a pile of skulls.