Why is it "reasonable"? Where do you find grounds to believe spirits care what language one speaks, does God?
Is the name of Jesus spoken in English less powerful than when spoken in Latin?
The problem is Catholicism is a faith with much of its doctrine built on the speculation of men and what sounds "reasonable" or "likely " without a foundation in the word of God
The grounds are simply in the statement by an old priest in this article. He has performed thousands of exorcisms during his life. He has an intimate knowledge of evil as his speciality. We can believe him or not. I do not intend to experiment with evil and try a few exorcisms and see if he is right or wrong. I take his word for it. That seems reasonable to me.
Biblical grounds - Scripture does not suggest what languages to use for exorcism as far as I know.
Is the name of Jesus spoken in English less powerful than when spoken in Latin?
I think it is the same. The article is about an series of exorcisms and lengthy exorcism prayers using one language over the other. It is not limited to the holy name of Jesus. The exorcism prayers are not a series of Jesus-Jesus-Jesus, until demons depart.
The best answer I have for why it could be more effective is simply related to the diabolic itself. The diabolic is all about destruction, disorder, disunity, disorientation, disequilibrium, and all the opposites to unity or union with God. Latin represents the official language of a unified Church. Therefore Latin is spoken as the Churches language and represents unity versus a diversity of language. Outside of this I think we need to ask the priest.
The problem is Catholicism is a faith with much of its doctrine built on the speculation of men and what sounds "reasonable" or "likely " without a foundation in the word of God
This is not a doctrinal issue, but one of specialist in his field observing results.