I made the changes to pt-BR locale according to Teo's suggestion and commited them to SVN.
However, there're some issues:
1. Clicking on the "Tips" button for the first time with a clean profile, results in a window too small.
I may debug it to find out how to prevent that.
2. After resizing the window, if we click on a link, it opens the Wikipedia's page inside the iframe, replacing the previous text.
IMHO, those links are not needed because the text already lists examples of diacritical marks, diaeresis marks and ligature marks.
3. IMHO, the white background doesn't look good on a dialog window.