I was very surprised to see that I couldn't revert, the only languages available were: German, Italian, English and Turkish.
I'm not sure where this information is coming from, but when she first started the phone it had a portuguese (although we were in Germany) and we had the option to choose portuguese in the installation language. So maybe the options are retrieved from within the card.
I was about to replace the card by another just to change the locale, but instead found this great app: MoreLocale 2
It unblocked a long list of options, including Portuguese from Portugal.