REST API Setup & Text Migration

I have an existing JavaScript code-base that currently pulls data through a few ad-hoc calls and still contains a fair amount of hard-coded UI text. I now need a clean REST API configuration that focuses on reliable data fetching and manipulation, and I want every remaining string migrated out of the source files into a single, easy-to-maintain location (JSON, i18n file, or any structure you recommend).

Here’s what success looks like to me:
• A well-documented REST configuration (endpoints, params, sample requests) wired into the project.
• All hard-coded English strings removed from the JavaScript and placed in an external resource the app can load at runtime.
• No regression in current functionality—existing components should still display the fetched data exactly as before, just now driven by the new API layer and externalised text.
• Quick rundown of how to add new endpoints or update the text file so the team can extend it without diving back into the code.

The repo is on GitHub, the app builds with Node and a standard Webpack setup, and I can give you clear examples of the current fetch logic plus a list of the files where text lives. If you’ve handled similar refactors or localisation-prep work, I’d love to see it—otherwise just outline how you’d tackle this and an estimated timeframe.