The vowel shift in plans (to plens) is common in lots of accents. It was standard upper class a couple of generations ago (listen to old movies - or Noel Coward) and you still get it in some circles. And you get it in accents in Southern Africa, both South Africa and in places like Botswana.

Accents are fascinating. I'm always puzzled at the way you can hear people talking, and recognise what language they are talking, and even what accent they have. Though there are some ways of talking where I have difficulty recognising either of those. I'vex been in trains where I've heard people talking, and only after a while realised they are native English speakers.