Check the folder aquasuite\database. There you will find a MS Access database called aquasuite.mdb. It contains the strings and you can add a new language.

Just to improve your understanding:
The aquasuite will include the new language in the firmware of the aquaero if you flash the aquaero again with the actual firmware after selcting the new language in the aquasuite.

The database can be edited with Access as Shoggy said.