Clozemaster already offers this for over 100 language pairings via the Fluency Fast Track feature, https://www.clozemaster.com.

Clozemaster's a game to learn and practice a language in context. The objective is to fill in the missing word in a given sentence for thousands of sentences. The missing word is the most difficult word in the sentence according to a frequency list for the language, and the Fluency Fast Track feature allows you to play a sentence for each unique missing word in order of difficulty like you described.