Hi - is Polish one of the supported languages, and where can I find a comprehensive list of supported languages?
Polish is indeed supported, including a full conjugation dictionary. For conjugating languages with cases (such as Polish, and most other eastern European languages), you will definitely want to have a look at the conjugations Help page.
I just noticed that the exhaustive list of languages was indeed not present on our new frontend website. It is now added to Features
Keep in mind that all these new languages are still in beta release. We expect some occasional glitches relating to pecularities of each language. So any feedback is welcome.