Edit and use your Japanese user dictionaries on Mac
After you set up a Japanese input source, you can add words, lists of words, or symbols to any of the Japanese dictionaries. You can also export your dictionary as a backup or to share it, and import dictionaries.
Add words
On your Mac, switch to a Japanese input source.
Click the Input menu in the menu bar, then choose Edit Text Substitutions.
In the Text Replacements dialog, click
.In the Replace field, type the hiragana reading of the word (up to 32 characters).
If you add an adjective, enter the reading in its dictionary form. The ending must be 〜い (~i). For example, あたらしい (atarashii) or たかい (takai).
If you add an adverb, don’t include inflective endings, such as 〜な (-na) or 〜だ (-da).
Click the With column, then type the replacement word (up to 64 characters).
Click Add.
Delete words
You can delete words from your Japanese user dictionary (but not the basic dictionary). You can’t undo this action.
On your Mac, switch to a Japanese input source.
Click the Input menu in the menu bar, then choose Edit Text Substitutions.
In the dialog that appears in Keyboard settings, select the word to remove, then click
.
Add frequently used emoji and symbols
On your Mac, switch to a Japanese input source.
Click the Input menu in the menu bar, then choose Edit Text Substitutions.
In the Text Replacements dialog, click
.In the Replace field, type the hiragana reading for the symbol.
Click the With column, click the Input menu in the menu bar, then choose Show Emoji & Symbols.
Find the emoji or symbol you want, then click it.
Click Add.
Export or import user dictionaries
On your Mac, switch to a Japanese input source.
Click the Input menu in the menu bar, then choose Edit Text Substitutions.
In the Text Replacements dialog, Command-click each word you want to export, or press Command-A to select all of the words.
Control-click the selection, choose Export, choose where you want to save the export, then click Export.
The backup file Text Substitutions.plist is created. You can edit the file using TextEdit.
To import a Text Substitutions.plist file, drag the file into the Text Replacements dialog of Keyboard settings while using a Japanese input source.
When you’re signed in to the same Apple Account on your Mac and other Apple devices, your user dictionaries are automatically updated and available on those devices. To see your dictionaries on your iOS or iPadOS device, go to Settings 
> General > Keyboard > Text Replacement.