I guess it depends on where in Portugal do you live. There are certain areas of Portugal in which swearing is regular, kind of the way it is in Spain; the curse words simply don't have the "heavy" linguistic and social connotations everywhere, for instance, in the Porto area it is quite offensive to call someone "gajo", which in the southern Portugal is not only not offensive as it tends to be the norm when talking about someone (trust me, I wasted years of my life in college studying "bolsas linguísticas por região").
Still, whatever your case may be, I was never really fond of the automatic "Portuguese" setting of the Worms' games of the past; if you decide to play a quick match against the CPU there's no way, to my knowledge, to change the default language, and it will *always* be BR-PT, because the game detects you're playing on a PT-based OS (even if it is PT-PT and not BR-PT). You can edit every team's soundbank, though, and give them English voices, so, if you plan on playing with your little sister and don't really want her to keep listening over and over again to the annoying Brazillian Portuguese speaking worms saying "que f*da!", I'd recommend against playing quick matches; take your time editing teams so that none of them uses the Portuguese soundbank or, better yet, create all new teams with the soundbanks of your preference.
I'm assuming you're referring to Worms World Party Remastered, so, if you're talking about any other Worms game, please let me know so I can help you on how to create and edit teams any further.
is there a way to do this in Armageddon? I tried editing the default teams (CPU1 etc) but quick play, deathmatch and missions use custom teams like Royalty and they all have the annoying default language voice. I looked through the game files but didn't see anything obvious.