I learned Yiddish because my aunt speaks it, and my cousins speak it, but I don’t speak any particular dialect of Yiddish, and I would describe myself as “conversant,” rather than fluent. I read and write Hebrew, but I don’t speak, which is another thing altogether. It’s possible to be literate in a language without knowing how to speak it-- and FWIW, I know biblical Hebrew-- I have trouble with a modern Israeli newspaper, although I think if you plopped me down in Jerusalem, I’d probably learn faster than someone starting from scratch. I also read Latin, but don’t write it very well. I get declensions mixed up too much. But few people outside the Vatican speak Latin. Probably 97% of people who know Latin well are only literate and don’t speak it.
Conversely, I am fluent in American Sign Language, a language that has no written form. I had total immersion in it when I was at Gallaudet University, and I can’t stress the importance of immersion enough. Immersion + motivation can produce fluency in a year. I had one year of classroom study that amounted to three hours in class, three hours studying videos, and three hours of practice with other beginners, per week, followed but total immersion, including classes with Deaf professors I’d bloody well better understand if I wanted to get good grades-- well, I also had a 3-week summer program at Gallaudet for new signers before the first semester started.
I took French, also, in high school and college, and I used to speak in passably, but I don’t anymore. However, I do still read it.
It is probably different now that people can travel, but Eastern Europe used to be full of people who can read English but can speak it.
One thing about English and English speakers: I’ll bet we can code switch and understand different dialects in a way that people whose native language isn’t so widely spoken don’t dream of. I mean, I once went to London, and could understand a guy in Limehouse who I think was a little drunk, and have 5 or 6 teeth. I can understand Monty Python, and* Priscilla, Queen of the Desert*. I can understand people from Appalachia, border neighborhoods in Texas, people with Cajun accents, and people from Jamaica. My mother is a linguist, and calls switching among dialects “code-switching.” I’ll bet native English speakers excel at this.
What’s more, we can understand all those people who learned English as a second language. It may not be as hard as learning a second language, but it is a skill in itself. My mother, who herself speaks 8 languages, also excels at deciphering people who learned English from a record. My Deaf friend from Sweden, who I used ASL with, and had no trouble signing with, but could not understand her recent efforts to speak English (she was fully literate in it, and apparently spoke Swedish pretty well, and had a Sheldon Cooper IQ, but with Penny social skills) had her first successful spoken English conversation with my mother. Anyway, my mother is fully qualified to say that this is a skill.
Some Americans are xenophobic, but on the whole, Americans are pretty patient which 2nd language English speakers. You can’t discount that.
OK, TL;DR, so I’ll shut up now.