I have tried with the Nim freetype library, but it does not work and there is no documentation.
I found this page with an minimal example: https://ralsina.me/weblog/posts/playing-with-nim.html
But it does not integrate with opengl and is not complete.
I have no experience with nimx, but I think that's the recommended library for that sort of things https://github.com/yglukhov/nimx
That answer seems to be very wrong.
NimX is a complete native Nim GUI toolkit. But He asked only about displaying text in openGL. Maybe SDL has functions for text in SDL, but I don't know.
haven't used it but there is -- https://github.com/jackmott/easygl