Change language of whole react-native app

My app in react-native has 2 languages: english and french. I've done a i18n.js file and 2 "translation.js" files for english and french. It's working great (i've tried it setting french on my phone, english on the emulator).

Now, I want to make a button in the app's settings to change the language of the entire app for the user but I don't know what function call and how to create this.

Can you help me ? Thanks a lot for your time and help.

my i18n.js file;

import i18n from "i18next";
import detector from "i18next-browser-languagedetector";
import { reactI18nextModule } from "react-i18next";
import { NativeModules, Platform } from "react-native";

import en from "../public/locales/en/translation.js";
import fr from "../public/locales/fr/translation.js";

// the translations
const resources = {
  en: {
    translation: en
  },
  fr: {
    translation: fr
  }
};
const locale =
  Platform.OS === "ios"
    ? NativeModules.SettingsManager.settings.AppleLocale
    : NativeModules.I18nManager.localeIdentifier;

i18n.locale = locale;

i18n
  .use(detector)
  .use(reactI18nextModule) // passes i18n down to react-i18next
  .init({
    resources,
    lng: locale.substring(0, 2),
    fallbackLng: "en", // use en if detected lng is not available

    keySeparator: ".", // we do not use keys in form messages.welcome

    interpolation: {
      escapeValue: false // react already safes from xss
    }
  });

export default i18n;

And I'd like to change the language from my Settings.js file :

<SettingsList.Item
              // icon={<Image style={styles.image} source={require('../../assets/images/icon_vol-mute.png')}/>}
              title={i18n.t("settings.action.languages")}
              hasNavArrow={false}
              switchState={this.state.activeSwitch === 3}
              switchOnValueChange={this.switchThree}
              hasSwitch={true}
              onPress={() => Alert.alert("French / English")}
            />

If you are using i18next

you can i18next.changeLanguage use to change your language

export const changeLanguage = (languageKey) => {
i18next.changeLanguage(lng, callback) // -> returns a Promise
}

import { changeLanguage } from 'services/translation';

<Button onPress={() => {changeLanguage(languageKey)}} />

But i recommended change to use react-native-localization instead of i18next by simply in implementation and native performance

How to use react-native-localization?

Installation

yarn add react-native-localization --save

#react-native >= 0.60
cd ios && pod install && cd ..

#react-native < 0.60
react-native link react-native-localization

Declare your translations

import LocalizedStrings from 'react-native-localization';
import english from './en.js'
import french from './fr.js'
import korean from './kr.js'

const strings = new LocalizedStrings({
 en: english,
 fr: french,
 kr: korean,
});

with en.js, fr.js, kr.js are the files contain your translations in key value format.

eg: content of fr.js

export default {
ok: 'D'accord',
no: 'non'
}

You can also use json file type for declaration.

usage

import strings from 'services/translation';

<Text style={styles.title}>
  {strings.ok}
</Text>

Change languages

write a function to change your app language and use it in every where you want.

const strings = new LocalizedStrings({
 en: english,
 fr: french,
 kr: korean,
});


export const changeLanguage = (languageKey) => {
strings.setLanguage(languageKey)
}

import { changeLanguage } from 'services/translation'


<Button onPress={() => {changeLanguage(languageKey)}} />

Notes: Do not declare key same at default methods like setLanguage

See more about react-native-localization here