I could see the voice actor learning a sentence or two but on occasion the bit goes on for a couple minutes. I feel like with a cartoon it wouldn’t be that hard to find a stand in who sounds close enough or use whoever does the dubbing for that language.
The only example I personally encountered “in the wild” was Disney’s Tarzan, where Phil Collins insisted on singing the songs in different languages himself. It was a bit surreal to hear him sing in German, and frankly it is very noticable that it isn’t his mother tongue.
Just in case you want to listen to an example: “Son of Man”, sung by Collins, in …
…German: https://www.youtube.com/watch?v=AbfGOohwP_4
…Spanish: https://www.youtube.com/watch?v=5k8NySrpplY
…French: https://www.youtube.com/watch?v=J5Oz2fBXTDs
…Italian: https://www.youtube.com/watch?v=1NpGoEpMZh4
On the other hand, I do appreciate the effort. Letting someone else do it would have been easier for him, but instead he sat down and learned a ton of phonetical lines by heart, in four different languages - none of which he understands. For all seven or so voiced songs in the movie.