Having been a non native speaker, several times I had been asked to write my name IN VERNACULAR or IN MOTHER TOUNGE during my college days. I couldn't tell apart the subtle difference and thought of them to synonymous those days.

Which out of the two is more formal to denote one's first language? ( I ask this as the term vernacular has derogatory connotations too) on the contrary, I thinkvthat mother tounge is a subset of vernacular and not vice versa.

Also, I personally of the opinion that using the word vernacular indicates imperialistic approach of the instructor as witnessed by the excerpts given below. (I m taken by the retro- noir- word "ANGLO- VERNACULAR")

Woods dispatch:-