Fix CoreNLP highlighting test and expand them to support multiple languages

As part of #529 (closed) I have added tests for the new Highlighting API, but they won't work on CI if we use the "Stock" CoreNLP flake, which runs a "multi-instance" that bundles EN and FR models.

I will update the test infra to deal with the multiple languages (like we do for production as well), and I will expand the test selection to include tests for FR (which at the moment have been marked pending)