Can you ask him about nursery? Also ask the staff what he likes to do - usually they take photos and ought to be writing up little reports and reviews on the children.
The language shouldn't really be a huge thing - kids do catch up incredibly quickly, and often understand a lot more than you give them credit for.
DSs school had a high % of EAL kids - you would have some every year who would be enrolled in the school with little/no English. It is amazing how quickly they adapt although, there was often issues with aggressive/violent behaviour as a child who cannot communicate will act out in frustration.
Your little one sounds like many nursery children to be honest. He's not been there long and its usually week 2 when happy kids become screamers - no idea why, but I assume once the novelty has worn off, they realise that home is rather nice as all their toys and mummy are there!
Speak to the staff. Teach them basic words and ask them what words you need to teach your child as a matter of urgency - so if he cant say 'I want the toilet' can you imagine how frustrating it is if he is telling them that and they are saying 'you want teddy? Drink? Book?'.
If you aren't happy that they can help your child with his language and that he is getting upset, consider looking around for other nurseries, possibly with other children/staff from your home country. It wont effect his English acquisition but will help him when he needs it.
I have to go and get my DS now, but please don't feel upset. They all cry at some point - it is heartbreaking but he wouldn't have been left in a cold dark corner alone. A member of staff probably gave him a cuddle, talked to him and tried to give him a toy or snack.