I'm a tool person, so I really like the idea of using your tools to push yourself forward in your language learning. It's hard to say how it would turn out in practice, but I'm optimistic.

As you mention, mixing vocabulary in languages that have very different grammars could become a bit strange, but code-switching -- that is, jumping back and forth between languages - is common and frequent with bilingual people, and it frequently happens mid-sentence, so I guess that just shows that people are pretty good at making it work even in radically different languages.

The area where I live has mostly Chinese Hongkongers, but many of them speak a lot of English in the office and at home, and it's pretty fun to listen to the kids on the playground and in the playroom talk to each other -- it's a real soup of Cantonese and English.