This priest obviously thinks he has greater authority than has been given him. I would go to a different Mass and tell him why.
The Traditional Latin Mass is immune to this knd of problem.
Never heard of such a thing happening. The TLM/EF priests of today are scrupulously (in the good sense) concerned with keeping things intact and unchanged.I doubt it would be immune. A short time with a Latin dictionary (if even necessary for a priest) would provide any extra words / phrases and a good proportion of the congregation might not even notice. Those that did would then be asking the same question as the OP…
I’ve always gotten the “vibe” that priests who tinker with the prayers of the Mass are trying to “make a point”, either to assert their own “slant” on liturgy or theology, to “educate” or “inspire” the faithful assembled, or both. I knew of one priest who, in reciting the eucharistic prayer, followed it word-for-word, until he got to the consecration of the Precious Blood. Then, time and time again, he very precisely and deliberately said “…which will be shed for you and for all people, so that sins might be forgiven”. He did this both prior to, and after, the 2011 re-translation of the Roman Missal. I hate to say this, in that he was otherwise one of my favorite priests — I talked to him a few days before he died — but somebody really needed to make a sub rosa recording of this, and share it with the bishop. As deliberate about it as he was, I really don’t think this priest would have, upon being asked about it by a layman, slapped his hand upside his head and said “you know, you’re absolutely right, I shouldn’t do that, I’m going to cut that out right now, thanks so much for correcting me”. Not hardly.