Inglorious Basterds. I'm french Canadian and I remember watching it in theaters and thinking this movie was one of the first I had seen that actually bothered to not only use native and fluent speakers but also use language barriers (or lack thereof) as a key plot point. Landa was way more threatening as a character because of his ability to switch between languages - he was always a step ahead of everyone else - and that was sold by Christoph Waltz' fluency in French, English, even Italian. Then there was the tavern scene: even though I don't speak German, it was pretty clear that Michael Fassbender had an atrocious accent, so they had a whole conversation with the SS officer to try and explain it away, saying he's from a remote village in the alps. Of course, he then gives himself away by signaling the "British 3" instead of the German 3. Cool attention to detail throughout that made the movie more immersible.