I added new user defined dictionaries to libreoffice 25, but when I tried to add a word to it the dictionary does not appear in the list. It also it put Slovenian and Hungarian dictionaries in the install although I never asked for them. LibreOffice 25 seems to be a total bust for me.
You must search for an archive with the name standard.dic , generally located in the wordbook dictionary folder, if it does not exist you must create it.
If it is an archive in text-only format, with a prior attachment as follows:
OOoUserDict1
lang: <none>
type: positive
---
A continuation of this entry must be the list of words, in column, it is in this archive where the personalized words are placed.