You know that I must have been a Lefty in college in the 1950s. I studied Russian.
Russia or the USSR, seemed to have an important future. I never doubted it.
Learning Russian was not a total waste. It was actually helpful to read some of the few great Russian writers.
On the other hand there are people today with the same blind perspective on the future that I had.
Some students in the 1970's and 80's were learning Japanese. Japan was clearly going to be number 1. There are some who are now teaching themselves or their offspring Mandarin. Same misguided view of the future.
If I had stopped to think at the time, or for that matter was capable of thinking in college, I would have realized that French had survived into the middle of the 20th century even though France had not been a world power in the previous 75 years.
This is of course a prelude to a discussion of English. It is unnecessary to learn other languages if one is an English speaker. However there is a vital necessity for learning English for non-English speakers.
This is all by way of saying in comparison to French which lasted a century after France was a modest world power, English could well last several centuries or more after it is no longer the language of the World's Central power.