I just re-read Shibumi by Trevanian, probably better known for The Eiger Sanction. The protagonist, Nicholai Hel, teaches himself Basque while in prison using a bilingual dictionary and some other books, so he has no description of the pronunciation, much less actual Basque speech to serve as a model. He therefore has to guess at the pronunciation of the alphabet. For the most part, he does well since Basque follows fairly closely the usual conventions for Western European languages, but he guesses wrong for the letter x, which he takes to represent the voiceless velar fricative [x]. In fact, in Basque x represents [ʃ]. He later goes to the Basque country and is exposed to the living language. He becomes fluent in Basque, but never overcomes his erroneous decision to read x as [x] and so has an idiosyncratic pronunciation. I wonder whether this has happened in real life? Pronouncing a written language incorrectly happens all the time; what I wonder is whether it is possible for such a reading pronunciation to become so firmly fixed that subsequent intensive exposure to the spoken language does not correct it, even in a case such as this where the correct sound poses no problem for the speaker?