i18next comes with a lot of modules to enhance the features available. There are modules to:

import i18next from 'i18next';
import Backend from 'i18next-http-backend';
import LanguageDetector from 'i18next-browser-languagedetector';
import sprintf from 'i18next-sprintf-postprocessor';
.use(Backend) // or any other backend implementation
.use(LanguageDetector) // or any other implementation
.use(sprintf) // or any other post processor

For usage details please read the documentation of the plugin (readme file in the repository or npm website).

If you're not sure on why you may need such a plugin, have a look at the First setup help page.