react-i18next documentation

The provider is responsible to pass the i18next instance passed in by props down to all the translate hocs or I18n using react context.
import React from 'react';
import ReactDOM from 'react-dom';
import { I18nextProvider } from 'react-i18next';
​
import App from './App'; // your entry page
import i18n from './i18n'; // initialized i18next instance
​
ReactDOM.render(
  <I18nextProvider i18n={ i18n }>
    <App />
  </I18nextProvider>,
  document.getElementById('app')
);
For the i18n instance have a look at the i18next instance page.
The I18nextProvider props:
name
type (default)
description
i18n
object (undefined)
pass i18next instance the provider will pass it down to translation components by context
defaultNS
string (undefined)
optionally pass down a default namespace to your translate HOC, I18n render prop (without having to specify it there)
initialI18nStore
object (undefined)
pass in initial translations (useful for serverside rendering)
initialLanguage
string (undefined)
pass in initial language (useful for serverside rendering)

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i18next instance

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I18n (render prop)

name	type (default)	description
i18n	object (undefined)	pass i18next instance the provider will pass it down to translation components by context
defaultNS	string (undefined)	optionally pass down a default namespace to your translate HOC, I18n render prop (without having to specify it there)
initialI18nStore	object (undefined)	pass in initial translations (useful for serverside rendering)
initialLanguage	string (undefined)	pass in initial language (useful for serverside rendering)