I hate how it says "Reply" where it should say "Quote" (to match "+Quote"). So, this is a quick tutorial (2 minutes) that shows you how to do make these changes.
First, login to your ACP.
Navigate to Appearance > Phrases.
Go to the search bar and tick the 'prefix match' box. Search for 'reply' .
The phrase that shows up first is the one you need to click on and modify.
Do not change the title of the phrase leave it as reply.
Go to the Phrase Text section and change the text from 'Reply' to 'Quote' or whatever you want to call it.