A clan can contain members that use any language. It’s also possible for a user to be in multiple clans.
Look at Example Clan: https://codecombat.com/clans/5530587343b9be960621cb64
Which should be the best language to start? The age of our students are between 9 and 12
Python is a very good language for beginners: it’s easy to learn, easy to read, flexible, with lots of handy stuff. Very good for a solid basis.