xumus,
Thanks for getting in touch! Unfortunately, the Community Add-on doesn’t support the submission of custom taxonomies. If this is something you’d like to see in a future release, I would suggest submitting it as an idea on our UserVoice page. Our team periodically reviews the most popular ideas for possible inclusion in a future release of the plugin.
If you have PRO, a possible workaround might be to use an ‘Additional Field,’ since these automatically display on the Community submission form (screenshot).
Hopefully that helps to answer your question, but let me know if I can assist further. Thanks! 🙂
-Casey-