Each culture throughout the world will be completely different and whilst up front, some may seem friendly than others, this is not always the case. Every person that lives on this planet is welcoming and will prove to be a great person to know but in some communities, some people may remained reserved until they feel comfortable with an individual.
It may take some time to get used to the attitude of different countries but overall, this is something you will grow to accept and the number one rule is if you treat people with respect, then there will be the same to you.
One thing that can work wonders is if you end up in a non English speaking area then make sure you are armed with a Portuguese dictionary. This can help and with the locals, if you get the dialect slightly wrong, they will certainly appreciate you trying.