Something I have always been interested in is developing videogames with the idea of teaching another language as a goal. Imagine a game such as Skyrim, a rather large and open world, but designed such that its goal was to teach you another language as you played the game.

Of course one can just change the language of the actual game Skyrim, and this is decent for learning new medieval themed vocabulary, but imagine if the game were designed with the concept of language learning in mind.

At the beginning of the game, the characters would speak clearly and with simple vocabulary. Perhaps with subtitles of written text in the same language. Maybe even with an English (or whatever your native language is) subtitle if you are really having trouble with a task.

The vocabulary used would go along the same pattern of reinforcing while slowly building more.

I think it might be a neat concept to explore, to learn a language passively while playing a fun game.