Portuguese characters

I am starting a blog in Portuguese (writing from the U.S.) and, even though the site is already using the Portuguese option, I cannot write any of the special Portuguese characters, such as ? and á. It only works if I copy those characters from other software (such as MWord). The keyboard tricks to write those characters (such as ctrl + , + c = ?) do not work in WP (for writing posts, writing comments, etc). How to make those keyboard tricks work in WP?