What did his mother call Jesus?

That old Texan joke: "If the English of the King James Bible was good enough for Jesus, it's good enough for me!"

I understand the local priest's attachment to the Latin Mass. Two thousand years of cultural continuity;  the kinship of fellow-priests down the centuries reciting the same liturgy.

Outreach into the vernacular must have seemed like wanton cultural vandalism.

Still, one should be mindful of the culture within which one basks. The Mother of God did not call her son Jesus (Ἰησοῦς in the language of the hated Empire) - it was the Aramaic Yeshua.