Display Rich Menu to match the user's device language

richmenu.js

const functions = require("firebase-functions");
const request = require("request-promise");

const LINE_MESSAGING_API = "https://api.line.me/v2/bot";
const LINE_HEADER = {
  "Content-Type": "application/json",
  Authorization: "Bearer YOUR-CHANNEL-ACCESS-TOKEN"
};

exports.LineBot = functions.https.onRequest(async (req, res) => {
  const event = req.body.events[0];
  if (event.type === "follow") {
    const userId = event.source.userId;
    const profile = await getProfile(userId);
    linkRichMenu(userId, profile.language);
  }
  return res.end();
});

const getProfile = (userId) => {
  return request.get({
    headers: LINE_HEADER,
    uri: `${LINE_MESSAGING_API}/profile/${userId}`,
    json: true
  });
};

const linkRichMenu = (userId, language) => {
  let richMenuId = "YOUR-EN-RICH-MENU";
  if (language === "th") {
    richMenuId = "YOUR-TH-RICH-MENU";
  }
  request.post({
    headers: LINE_HEADER,
    uri: `${LINE_MESSAGING_API}/user/${userId}/richmenu/${richMenuId}`
  });
};