Hello, I am a Karaite Jew who is interested in languages. In Crimea, there are several ethnic groups with different languages and cultures.
During 1600s all these ethnic groups were under a rapid Tatarization process, for instance, Urums a Greek ethnic group in Crimea today speak a Tatar dialect and almost half of them are assimilated into Crimean Tatars which today they known as Yaliboyu Tatars (Coast Tatars). Centuries after Crimean Khanate, some Urums started speaking mainland Greek language to preserve their identity.
On the other hand, there are people known as Crimean Tat people (a branch of Crimean Tatars) who are descendant from Crimean Ostrogothic people who were Tatarized, their region called Magnup Qale which means the Castle of Gothia. Today, Karaites can speak Israeli Hebrew, Urums can speak mainland Greek but Tats cannot speak Gothic (because it's extinct) or they cannot claim to be descendant from Goths even tho they have ancestry from Goths.
Today Gothic language extinct therefore Gothic people extinct too, even they exist with a different language. I first thought Gutnish is their mother language. Can we say language and ethnicity are necessarily directly related. While a certain language may be spoken by a particular ethnic group, it is possible for individuals or groups to speak a language that is not considered to be their ethnic language. But these actions soon or later intend them to be assimilated as far as i see.
There are dozens of different European settlers in US who trace their own ancestry from all over Europe but they use English as a lingua franka and they are just consider themselves as whites.