According to the uesp lore page on the dragon language, Dovahkiins is incorrect.



"The language has basically the same grammar as English, with the exceptions that it doesn't have an equivalent to English's apostrophes, it tends to place prepositional phrases earlier in sentences than English does, and it doesn't have tense.[4] To make a word plural, two letters are added to the end of the word, the first being the last letter in the singular form, and the second being an 'e'"



So I guess that would make it Dovahkiinne?



Yes I did too much research on the language of the dovah.