I had chickenpox as an adult (didn't have it as a child) at the age of 30, was not great, and then a month later I started losing my hearing (I am now partly deaf in one ear). The (Harley Street) doctors never found the cause for my hearing loss and one theory is that it was caused by the chickenpox, as there is some research linking serious viral diseases with this type of loss.
Needless to say, we vaccinated our daughter (you are meant to do 2 shots, after they are 12 months old). It is routinely offered in other countries and your child will have 98% immunity. Even if they are in the 2% who still get it, it will be very mild. Also don't believe the rumours that they can get shingles as adults - shingles is the chickenpox virus in your body re-activated, typically when your immune system is down (I got it soon after the birth of my first child as I was so run down and unwell).
The vaccine is not offered in the U.K. A) because there are already such issues with people taking up the MMR vaccine b) there is this "herd immunity" theory that says if enough people (children) get it it protects everyone: if you vaccinate all the kids, then the adults who didn't get it as children will get it and it will be much worse for them.
Here is a great Guardian article that talks about it:
https://www.google.co.uk/amp/s/amp.theg ... ent=safari
The bottom line: if you can afford it, I would vaccinate! We did it at the Wandsworth travel clinic (by Southside).