The Portuguese instruments I am familiar with are the Portuguese mandolin or Waldzither, and the Portuguese guitarra. There are two slightly different varieties of the latter, from Coimbra and Lisbon. These are related to the early English guitar or cittern, formerly found all over Europe and surviving now in Portugal and parts of Germany.
They share an onion-shaped body form, but have different string arrangements. The portuguese mandolin has nine strings in five courses, while the Portuguese guitarra has twelve strings in six courses. Not sure if the five courses (ten strings) of the Viola de Braguesa (or de Braga) follow the tuning for Portuguese mandolin. I used the four double courses as effectively mandola tuning cC gG dd aa with a lower G on the single string course. Wikipedia gives a tuning range for the Viola de Braguesa without much further detail.
Sorry can't help further. Where did you come across the instrument?