By the way, what do you think of my alternative interpretation of the names of places in Croatia?
Language similarities are mostly due to geographic similarity. If the two countries are geographically close, they will have similarities in terms of language. Turkish and Uighur come from the same root because Turks and Uighurs are close both racially and geographically. Just like many Turkish subcultures. Genetically, the affinity of Europeans with Turks is almost certainly proven today. Turks and Greeks are alike. Likewise, Greeks and Italians are alike. They lived together for a long time under Roman and Ottoman rule. They have both genetic and language similarities. Countries leaving Yugoslavia are similar. Therefore, it is not surprising that there is kinship between Russians and Croats of Serbian origin. However, this does not mean that they are traditionally the same language family. The place where lived for longer is decisive here.
Spaniards, French, Germans, and British alike because they are close. There are similarities between Tunisia with Spaniards, and Libya with Italians and Turks. For example, although Iranians are an ancient civilization just like the Turks, there are many common words between Persian and Turkish. Indians, a separate race like the Persians, have many common Persian words. It is all about geographic proximity.
When a country invades another country, it carries its culture and language there. With marriages, that language becomes a second language. And some words start to become common.
For example;
"Salam" is an Aramaic word, common in Arabia and Israel. But we Turks also use it, because of we have lived together for a while. And you can see it some other countries even not muslim, but because learned from Turks. "Merhaba" also is a well known Turkish word comes from Arabic. It means "mer" (means you in Persian) and "haber" (means news in Arabic). It combined Persian and Arabic word, but known as Turkish. Because when persians occopied Turkey until Ankara for a while, they have carried their language also.
There are 15 millions of Azeri-Turks in Iran.
Summery,
I have no idea rationally where Crotians belong to. As far as I see, it is a subculture affected by others around.