The Rivers of London series by Aarnovitch includes it a lot. The training of a wizard definitely requires Latin, with some other languages being very useful and occassionally needed. I hope this won't be considered spoiling, but the new book includes a funny bit, where teaching someone to write the terminology in Cyrillics with abbreviations instead of Latin in full words is seen as a bad practice and something to worry about. The main protagonist is starting Greek now in book 7 and needed bits of German with a dictionarya few times in past. And I guess his Master may push him to French and German learning one day too, who knows, especially German
The learning process is not unrealistic here, with the busy supernatural policeman having to find time for his grammar translation based studies.
Star Trek Enterprise is the opposite, with Hoshi Sato not just learning, but also decyphering completely new languages in a few days. A few hours, if the destiny of the whole crew, Earth, or the universe depends on it
A wonderful Czech scifi trilogy Propast Času (the Time Abyss) by Bureš is about a catastrophical event, in which various time periods get mixed. Like a patchwork, where the individual pieces of various periods are suddenly neighbours, people can travel across the borders and they have to live together or perish now. A Czech archeology student suddenly finds her Latin (which she has to improve significatnly, through immersion), English, and German skills crucial for her survival (and a few more languages would be very useful in her situation), rise to power, and building a new world. The other characters need to learn too, as they are suddenly living in a widely multicultural society, and some of them struggle in an amusing way. I don't want to spoil it for any random Czech learner (I know there are a few and this trilogy is one of the very best our fantasy can offer you know. I've recently updated my knowledge of the contemporary authors), but there are a few awesome scenes we all know damn well, when someone doesn't know you can understand and talks absolutely horribly in your presence, thinking they're protected by the language barrier
Hey, I can't resist it,Czech learners look away: there is a scene, where our heroine sits on the throne of the New Rome she's built (consisting mainly of ancient romans) and a British delegation (from the colonial era) arrives. And they talk very openly in English about how they're gonna profit from yet another stupid barbarian queen and abuse and drain the country. What a surprise, when the Roman Empress speaks a bit more modern version of English and she also knows all their strategies.
Yes, I thought of Artemis Fowl too. Sure, he is stereotypically genious, but I think that is fun and definitely not harmful. It's a fantasy book for older kids, it doesn't have to be realistic, the kids don't take any harm from it. And it definitely shows being clever and educated as a desirable and fun quality, which is always a good thing.
The Thirteenth Warrior, a movie based on a novel, where an Arab learns Norse by listening to others around him talking for a long time.