I don’t know the historic background, but I would totally believe this. I learned a little bit of spoken Tibetan while I was there, but the romanized words are not pronounced at all like they’re spelled and pronunciation is difficult in general. It wasn’t necessarily the language itself though, it was more that you have a break in concentration where someone is speaking Tibetan for 2 minutes while you stare at them, then you listen to the translator for 2 minutes and try to write things down, then it’s back to not understanding for another 2 minutes, etc. I imagine it’s a lot more effective when you speak the language. But 2 hours of that a day was really not fun. Still learned a lot though.