'LocalLibrary' file

Solution 1:

It's called LocalDictionary not Library & is just a plain text file, but has no .txt extension. I also have two others, called en and en_GB. I really don't know what the difference is, but they all contain different custom word lists.

Presumably, if there isn't one there already, you just need to create one.

If you don't want the task of doing that yourself, then right click any word the regular spellcheck doesn't like & 'Learn Spelling' - I'm pretty sure that should create the file & populate it with your first word.

One thing to note, if you're going the DIY route for this - words are in alphabetical order, not just added by date to the next line.