metamask-extension/ui/app/contexts/i18n.js

import React, { Component, createContext, useMemo } from 'react'
import PropTypes from 'prop-types'
import { useSelector } from 'react-redux'
import { getMessage } from '../helpers/utils/i18n-helper'
import { getCurrentLocale } from '../ducks/metamask/metamask'
import { getCurrentLocaleMessages, getEnLocaleMessages } from '../ducks/locale/locale'

export const I18nContext = createContext((key) => `[${key}]`)

export const I18nProvider = (props) => {
  const currentLocale = useSelector(getCurrentLocale)
  const current = useSelector(getCurrentLocaleMessages)
  const en = useSelector(getEnLocaleMessages)

  const t = useMemo(() => {
    return (key, ...args) => (
      getMessage(currentLocale, current, key, ...args) ||
      getMessage(currentLocale, en, key, ...args)
    )
  }, [currentLocale, current, en])

  return (
    <I18nContext.Provider value={t}>
      { props.children }
    </I18nContext.Provider>
  )
}

I18nProvider.propTypes = {
  children: PropTypes.node,
}

I18nProvider.defaultProps = {
  children: undefined,
}

export class LegacyI18nProvider extends Component {
  static propTypes = {
    children: PropTypes.node,
  }

  static defaultProps = {
    children: undefined,
  }

  static contextType = I18nContext

  static childContextTypes = {
    t: PropTypes.func,
  }

  getChildContext () {
    return {
      t: this.context,
    }
  }

  render () {
    return this.props.children
  }
}