If you say "other learners and teachers" this means "other teachers and other learners", so unless you are also a teacher, you need to rearrange them. I use the Oxford comma so would write "tests, and vocabulary" because usually the Oxford comma results in fewer confusing sentences. But you don't have to use it, just be consistent. "We use "advice" in the singular. Please let me know if you have any questions about my comments :) and I agree there is so many things to learn about other languages, places, and cultures here