144 has stumbled me a lot. Quran clearly states that 'We never sent forth any rasul (messenger) except in the tongue of his people....'
None of the classical interpretations in English have satisfied me, and enemies of Islam have used this to further their own aims.

Essentially there are two explanations that I am inclined to explore further...
Mohammed Asad in his footnotes for this Ayat writes;
Since every divine writ was meant to be understood by man, it is obvious that each had to be formulated in the language of the people whom the particular prophet was addressing in the first instance; and the Qur'an - notwithstanding its universal import (cf. note 126 on 715 - is no exception in this respect.
Here M Asad's explanation depends on the use of 'in the first instance' - not entirely satisfactory.

The second explanation hinges on the definition (and difference) between nabi (prophet) and rasul (messenger). The quran supports a difference in meaning here, and the most convincing (thus far to me) difference put forward is that Nabi brought a scripture/message (Prophet Muhammed, Moses & Aaron, Jesus, ...) and the role of the messenger is to clearly explain that message.
I believe knowing this distinction helps understand a lot of verses of Quran, which have perplexed me otherwise, and I also believe it may put you on the path of answering your questions!

I don't want to ever write anything that may mislead anyone hence I've left my remarks rather open ended for your research, but nonetheless felt compelled to write because I think your answer is in the second explanation (the use of word rasul).

Qamar