Kids like when things are organized (although they can sometimes create chaos). Here's the first way you can keep their book selections organized by language.
Why should I re-read the same books? Re-reading exposes your child to the same words over and over again. It gives them time to hear the word, understand it, and eventually use it.
Using words and illustrations in books, teach some of that missing vocabulary in an enjoyable, shared experience. No more forced speaking or disparaging. Subtle teaching, reviewing in context, and careful encouragements.