Userscript
If you know some coding, you can customize Scrapbox by adding style.css and script.js Code blocks to your Profile page. After adding or updating script, reload the page and you should see a message to Load new user script.
Note: Customization will only be visible to you.
Example:
Add a Google Translate Button (EN --> JA)
code:script.js
scrapbox.PopupMenu.addButton({
title: 'Translate',
onClick: text => window.open(https://translate.google.com/#en/ja/${text})
})