Using the web app Create React App I've showcased the i18n libraries FormatJS (react-intl), LinguiJS, and i18next. I take each library for a test ride in seperate branches and made sure that my commits are easy to follow for anyone learning to internationalize their own React app.
Visit the branch of the library you're interested in to see the commits and follow along. Or if you want to get your hands dirty, run npx create-react-app my-app and internationalize your own project by following a library's tutorial and referencing my commits when needed.