Some strings are left untranslated
The translation to spanish is really good until a few lessons in. The text start to switch from spanish to english on some paragraphs (i guess some are not translated). Another issue is a conceptual misunderstanding, translating "array" to "matriz" which is the spanish word for matrix. This is a big blunder, the correct word for array would be "arreglo"
Matriz is a correct translation for "array" in computer science in Spanish. You can look it up, you'll find many sources.
Regarding English strings, the issue is the need to update translation strings. We've been looking to automate the integration of updated translations with new releases but lack the time/budget for that and this system didn't get contributions either.
We constantly have too much on our plates, and right now this translation system is very low priority for us as we're focusing on making a new app and course for Godot 4, with a new technology.