Bug#898550:

[J. Smith]

reassign 898550 dictionaries-common
stop

Your backtrace indicates that the error comes from 
debian-ispell-preprocess-dicts-alist, which is provided by
debian-ispell.el from the dictionaries-common package. This is corroborated by 
the fact that the error disappears with -Q, which prevents loading of such 
site-lisp files. Perhaps the basic problem is using 'UTF-8 where 'utf-8 is 
needed.