The official acme client is certbot, which is a Python program.
I run that program to get my certificates and manually configure nginx to use them. They have pretty good instructions.
I use nginx as a reverse proxy and for SSL termination because I have various application servers running that all want to be exposed via virtual hosts. I don't think anyone has written such a program in Nim yet. I would be very interested to try one- you could write your configuration in Nim, and compile the server just for your setup!
So SSL doesn't usually touch my Nim directly, so it doesn't really matter that I have to run a python program every month to keep my certificates fresh. It might matter if your server doesn't have python.