The same problem as in the previous version.
Then I reported:
1-Sigil 0.5.3 ravage the user_dict.txt in words with accent (spanish).
2-Now I know what the problem with user_dict.txt
I open Sigil 0.5.3: Edit, Preferences, and I close this window .... and voila! the user_dict.txt is now encoded
UTF-8 without BOM.