stackoverflow-64896144

controllers.first\.js

import Controller from '@ember/controller';
import { inject as service } from '@ember/service';
import { action } from '@ember/object';

export default class FirstController extends Controller {
  @service settings;

  @action changeLanguajeToEN () {
    this.settings.lang = 'EN';
  }
  
  @action changeLanguajeToCN () {
    this.settings.lang = 'CN';
  }
}

router\.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

const Router = EmberRouter.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('first', { path: '/' });
});

export default Router;

services.settings\.js

import Service from '@ember/service';
import { tracked } from '@glimmer/tracking';

export default class SettingsService extends Service {
  @tracked lang = 'EN'
}

templates.first\.hbs

<div class="wrapper">
  <h3>First route</h3>
  <hr class="gold">
  <p>
  	<button type="button" {{on "click" this.changeLanguajeToEN}}>Change to English</button>
    <button type="button" {{on "click" this.changeLanguajeToCN}}>Change to Chinese</button>
  </p>
  <p>The current language is: <code>{{this.settings.lang}}</code></p>
</div>

{{outlet}}

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}