Got it!!
Searched more and found this: http://wordpress.org/support/topic/plugin-polylang-changing-theme-options?replies=5
I'll just leave a quick how-to, in order to help someone that may have the same issue:
You mentioned:
<em>Now you have to find where the string is displayed on frontend and replace</em>
And from this, on functions.php: pll_register_string('footer-mapa', 'mapa do site');
Added this, on the template that echoes the string I wanted to translate: pll__('mapa do site');
Many thanks for the help and, above all, many thanks for this great plugin!
Not sure if you want to mark this thread as resolved or if you need it to help qrmiz. There's no problem for me.
Regards,
André