How to deal with people from different cultures and countries?

The same way you would with anyone from your own culture, with respect and courtesy. Speak clearly and politely (if people have trouble understanding English, yelling it doesn't help), don't touch them if they don't touch you first. Be friendly and welcoming. Cultivating friends from various backgrounds is a wonderful way to enrich your life.

You need to be more aware and in-tune to how people from unfamiliar cultures or countries feel or act. Be aware of their body language to help ensure that what you say or do (or vice versa) is taken the way it was meant to be taken.

And don't be scared to ask questions.... Often time people are more than pleased to help you understand.