You don't need to know the students' languages, but some knowledge always helps as it enables you to see what problems they might face. If they come from other language families, then they may have considerable difficulties in assimilating the English system.
Do you have internet access? If so, then you don't need any outlay really- there's plenty of free stuff out there that they can practise on. If you could let me know this, then I can try to help with this, or, if not, try to suggest other alternatives.