I am sorry for the misunderstanding; my fault. Basic vocabularies do change; but they do not change unless some serious changes are taking place both ethnically and culturally. They make up the most resistant and stable part of every language. If there are borrowings to a basic vocabulary of a language, then I would think that the people whose basic-vocabulary-words are being borrowed are living very closely to the group that is borrowing these words – close enough that their kids may be playing together. A few borrowed words in a basic vocabulary are not a major thing – it might happen, but when it is the big portion of a language then there must be something unusual happening.
‘Sey’ is a very good example. It is Arabic; there is no question about it. I am very impressed with both your knowledge and curiosity in the linguistic matters. Turkish words do not start with n, m and z; you are correct. But y is not in this class. Turkish has a lot of words that start with y; it is a major initial letter. About n, however, there are a few exceptions and ‘nen’ is one of them. What did you do: took a Turcology class?
I do not like the idea of ‘original language’. It is eventually a social Darwinist and pan-something-ist idea. Did Gokturk speak a language that was more Turkish than ours? We will never know, because we have no way of comparing them with the groups that might have preceded them. They spoke their Turkic language and we are speaking our own kind of Turkic language. However, we might compare their basic vocabulary and morphology with what their neighbors might have had at the time, and do the same for ours, and then see who was purer. But, of course, I do not know what we can gain by this. Was it the only dialect? I do not know. Some say Oguz and other Turkic languages came after Old Turkic, and some say these languages were already there with the Old Turkic. It is a confusing subject. But, one thing is sure: gokturks were the only cultural group who called themselves Turks until the founding of our republic. There is of course the case of Turkmens. I do not think we will get too far by asking Turkmens, because we are really trying to understand the people who were called Turkmen in the 11th century, not the ones who go by the same name now. We need to go to the sources from the 11th century and try to understand the term according to its context. After all, how many of us know what Turk means? But, we are using it. Do you know Filiz?
Languages change. Everybody borrows. Some words die in time and some stick around. I do not really know the reasons. I will supply you with examples as I come across of them.