Author provides a convincing if not biased Review: https://medium.com/@jamuhl/i18n-frameworks-the-unfair-showdown-8d436cd6f470#:~:text=formatjs%20comes%20with%20built%20in,on%20the%20need%20of%20developers.
Author least has agnostic atitude: https://medium.com/@jamuhl/the-freedom-of-choice-i18next-polyglot-or-formatjs-8c479f9e6890
If nothing else, he is good at SEO.
**Supports translation outside of react: **
Is Trending better: https://www.npmtrends.com/i18next-vs-react-intl
component nesting
i18next :
https://react.i18next.com/latest/trans-component
vs format.js version:
https://formatjs.io/docs/react-intl/components/#rich-text-formatting
i18next version might be better
On the other hand, format.js has had some explosive commit activity recently: https://github.com/formatjs/formatjs/graphs/contributors