Crimean gothic, as it is called, is a rather unique example of a language that we have unfortunately very little knowledge about.
Sometime between 1555 and 1562, Ogier Ghislain de Busbecq, a diplomat from Austria, made some interesting notes about a language he encountered during his travels in the Ottoman Empire. Pretty much all we know about crimean gothic is recorded below.
Please note: There are a large number of suspected errors in the original manuscript, most of which are explained in their entries in the lexicon. One case of bad typesetting in particular seems to have had the result that several letters fell out and were placed back in the wrong places: For instance, we have kor and thurn instead of korn and thur, hoef and fisct instead of hoeft and fisch, &c.
Busbecq's Account of Crimean Gothic
Crimean Gothic Lexicon