Plot Labels with Special Spanish Characters

I can't write spanish characters like accents or the letter ñ in the axes labels.

I can write them in the corresponding string in the code, but they don't appear properly in the plot when I execute the function, (MatLab substitutes them for other characters)

Note: I work with Ubuntu and my system Lang is set to UTF-8 Thanks!

[Walter Roberson]

See also http://www.mathworks.co.uk/matlabcentral/answers/77112-why-matlab-does-not-show-the-special-characters-e-g-c-or