Use APKPure App
Get User Dictionary Backup old version APK for Android
Backup Your Custom Dictionary
UDB (User Dictionary Backup) allows you to Backup and Restore words you stored manually in the Dictionary. It also allows you to import words from a .txt list of words (each in a new line, placed in the "UserDictionaries" Folder.)
**This App might not work on Phones which provide their built-in Backup/Restore options for the User Dictionary.