Have you tried adding it via Preferences > Dictionary > plus sign to Add User Dictionary? Is it a purely txt file consisting of word entries separated by a hard return, and no other formatting or characters?
Yes. I had tried adding it via Preferences > Dictionary, but the same problem occurs (InDesign quits).
And there is no other formatting or characters in the txt file. It purely contains words separated by a hard return.
Windows or Mac? Version and patch level of ID?
This sounds like it might be a font problem, but you should try a new user account to see if it works there.