Translation:If I were pregnant I would marry Dewi Lingo.
Yes, 'if I were' works better and is a better translation of 'Taswn' isn't it? 'If I were pregnant I would marry Dewi Lingo'
It looks like they're using "If I was" now, which is not too horribly ungrammatical and much better than "If I would be." "If I were," is, as you say, better still, though perhaps not as common as "If I was."