I date from well before Vatican II, and traveled extensively during the 1950’s, 60’s and '70’s.
When the Mass was in Latin, it made no difference what country you attended it in, because it was the same all over the world. The pronounciation of the Latin words might vary, but if you had a basic knowledge of the Mass, you could understand it.
At that time, almost every practicing devout Catholic had a Missal, and used it. The Latin words of the mass were on one page and the approved English (or other language) translation was on the next page, side by side with the Latin.
When the Venacular Mass was ordered, all of that changed, except one thing…the need for a Missal if you are travelling to a foreign country in which you do not know the local language. If you have a modern missle in your own language, following the Mass is not that difficult.
I am a member of St. Stanislaus Bishop and Martyr Church in Manhattan, New York City, largely because I am 1st generation Polish/German American and I live only a couple of blocks from it.
They have only 2 Masses a week in English. I understand enough Polish to get by with relatives and in the neighborhood. But, it is not good enough to get full benefit from the Mass in Polish. That is why, when I have missed the 9 AM Sunday Mass in English and have to attend Mass in Polish, I follow it using the English language Missal provided in the pews.
It is the same when I attend the Rosary before the Saturday Vigil Mass which is in English. The Congregation recites the Rosary in Polish, but I am more comfortable saying it in English because that is the language in which I learned it.
If you attended Mass at St. Peters in Rome, chances are that it would be said in Italian. Your following it in English still would make it valid.