But for products aimed at end-users? Absolutely don't name it after the language it's written in.
To play devil's advocate for a moment though: this is the software used to run the forum for the language Nim. If you've ever been to the Nim forums, this is a version you can run yourself. Maybe that makes the name a bit more reasonable?
Certainly if there is interest I will happily consider rebranding.
NimSquawk?
from the very obvious to the whimsical:
NimmoPhon
Nimference
Nimbeaumôt [sic]
Nimditer
Echonim
Edit:
how I missed Nimsical, I don't know..
Nimminent
I am pushing it rather, so I'll quit while I'm behind... Sorry, but I have to try suggesting PhonoNim, after [0] thinking of phone typos in text conversations.
[0] https://www.urbandictionary.com/define.php?term=phononym
Kodi was previously XBMC which stood for "X-Box Media Center" long after the X-Box was no longer their focus of development (and perhaps even completely unsupported).
Your criticism applies equally to phpBB, and is valid. I suspect if NimForum becomes popular, the Nim part of the name will go away.