This is a bit curious. I have no time for these 'speak English or go back to your own country' racist buffoons. It's natural that you'd use whatever language comes the most naturally for you. Why would two Polish people (for example) converse in any language except Polish?
I agree. I had just met the idea several times over the years.
One day I was at university and we were walking to another class or something, two people were from Greece and having a conversation in Greek. One then stopped and apologised and said sorry that was really rude, I should be speaking to (my other greek mate) in English.
More recently a guy that runs a restaurant I do some stuff for was having a conversation in French with his sister or maybe aunt, he apologised to the others in the room for it afterwards.
In both cases there were three or more theoretically non speakers around and nobody even thought to be offended, to notion that someone might be being just as strange to them as me. I have met it several other times over the years but the first one was the first and many years ago and the other one was the last time a few months ago.
As for why then some people do it for practice, some people do it because it is easier (most scientific, technological and engineering literature being written in English and you might well have only learned the English terms is a big one, though in some cases that means alternating a lot) and I have also seen it where someone might have forgotten the language or become less able to keep up (usually someone that had been speaking it until somewhat recently vs someone that might have been somewhere else for decades).
First, that's not my accent, I have been told that I have overall a neutral accent.
I don't have a British accent in any way.
I was not saying you did, just that is the voice my head read it in/imagined it in.
On neutral accents I would say the only people I have met with neutral accents have been deaf people, everybody else tends to have something. Granted some people call a standard accent a neutral one, Americans in particular sometimes call various midwestern accents neutral which is a curious choice of words and also few would mistake someone with such an accent for anything other than American. Some even seem to get quite upset about that if you say they do have an accent.
In your case even without word choice or pronunciation choice* would someone from Brazil be able to tell you are from Portugal and not just someone that learned it from a book or something?
*if I don't know French to that level I certainly don't know Portuguese (I know the differences can be somewhat more extreme than French or English between old world and new) but there have to be some words, grammar choices and such that you could make a normal sentence that is the same in both.