I'm Brazilian and I'm writing a book in portuguese. However the story takes place first in Europe, i.e. Italy, Portugal, and London. Of course this requires of me some research about the culture of these places. After that it is going to take place in Brazil.
Besides that I have a little doubt about how to describe the language two characters would be speaking in, mainly if they speak multiple languages. SHould I always mention in which language the characters would be speaking everytime they change places? Should it be implied depending on the country the characters they are?
There are also somethings that make sense only in certain languages, like rhymes and contextual jokes. Should I write that it both the main language of my text and the specific language the character is speaking? Would not that become burdensome to the reader mainly considering that most of the readers won't be polyglots?
Example (in which English is the main language, but the character is saying something relevant in Portuguese):
And then the man said:
-Não se preocupe porque sempre chove quando menos se espera. (Don't worry because it always rains when it is least expected.)
Mark did not know what the man was saying. He only know it was Portuguese. He knew that "Não se preocupe" meant "Don't worry", but what about the rest? He hadn't the chance to ask, for the strange man couldn't be seen in front of him anymore...
Do you have some examples of stories following this pattern?