I live in Sweden which uses characters like Å,Ä and Ö. But when I try to use them in labels or in datapoints the letters get changed to '?'. How can I show those letters correctly?
I didn’t have any trouble getting the character in label.
But I don’t know what you mean in data points
I did not have any problem displaying them in R2018b.
A work-around is to specify: 'Interpreter','latex' in your xlabel, ylabel, title, legend and text function calls. See: The Not So Short Introduction to LaTeX2e to understand how to use LaTeX if you are not already familiar with it. (It is also a good reference even if you have experience with LaTeX.)