"Missing translation: navigation.subnav.textReplacements" when running an Ember acceptance test related to ember-i18n package

I'm writing acceptance tests for an Ember component which allows the user to toggle their i18n settings via a dropdown provided by the ember-select-list package. I'm also using the ember-i18n package for the i18n settings. The dropdown component looks like this:

import Ember from 'ember';

export default Ember.Component.extend({
  i18n: Ember.inject.service(),
  languagePreference: Ember.inject.service(),

  classNames: ['language-dropdown'],

  languageOptions: Ember.computed('i18n.locale', function() {
    let i18n = this.get('i18n');
    return i18n.get('locales').map((item) => {
      return {
        id: item,
        name: i18n.t(`languages.${item}`)
      };
    });
  }),

  onFinish: null,

  actions: {
    selectLanguage(i18n) {
      this.get('languagePreference').setUserI18nPreference(i18n);
      this.get('onFinish')();
    }
  }

});

The language-preference service looks like this:

import Ember from 'ember';

export default Ember.Service.extend({

  i18n: Ember.inject.service(),
  config: Ember.inject.service(),

  setSessionI18nPreference() {
    let setSessionI18n = (results) => {
      let { preferences, userName } = results;
      if (userName && preferences[userName]) {
        this.set('i18n.locale', preferences[userName].i18n);
      }
    };
    this._fetchUserPreferencesDB().then(setSessionI18n);
  },

  setUserI18nPreference(i18n) {
    let setUserI18n = (results) => {
      let { preferences, userName } = results;
      if (preferences[userName] === undefined) {
        preferences[userName] = {};
      }
      preferences[userName].i18n = i18n;
      this.get('config.configDB').put(preferences);
      this.set('i18n.locale', i18n);
    };
    this._fetchUserPreferencesDB().then(setUserI18n);
  },

  _fetchUserPreferencesDB() {
    let configDB = this.get('config.configDB');
    let userName;
    return configDB.get('current_user').then((user) => {
      userName = this._fetchUsername(user);
      let preferences = configDB.get('preferences');
      return Ember.RSVP.hash({ userName, preferences });
    }).catch((err) => {
      console.log(err);
      if (err.status === 404) {
        this._initPreferencesDB(userName, 'en');
      }
    });
  },

  _fetchUsername(user) {
    switch (typeof user.value) {
      case 'string':
        return user.value;
      case 'object':
        return user.value.name;
      default:
        return undefined;
    }
  },

  _initPreferencesDB(username, i18n) {
    let doc = {
      _id: 'preferences'
    };
    if (username != undefined) {
      doc[username] = {
        i18n: i18n || 'en'
      };
    }
    this.get('config.configDB').put(doc);
  }
});

For the acceptance test, so far what I have is this:

import Ember from 'ember';
import { module, test } from 'qunit';
import startApp from 'hospitalrun/tests/helpers/start-app';

module('Acceptance | language dropdown', {
  beforeEach() {
    this.application = startApp();
  },

  afterEach() {
    Ember.run(this.application, 'destroy');
  }
});

test('setting a language preference persists after logout', (assert) => {
  runWithPouchDump('default', () => {
  authenticateUser({ name: 'foobar', prefix: 'p2' });
  visit('/');

  andThen(() => {
    assert.equal(currentURL(), '/');
    assert.equal(find('.view-current-title').text(), 'Welcome to HospitalRun!');
    });
    andThen(() => {
      click('a.settings-trigger');
      waitToAppear('.settings-nav');
      // andThen(() => {
      //   select('.language-dropdown', 'French');
      //   andThen(() => {
      //     debugger;
      //   });
      // });
    });
  });
});

This works fine and all my tests pass. But when I un-comment the block that's currently commented-out, and re-run the tests, I see multiple test failures, starting with a global error:

not ok 66 PhantomJS 2.1 - Global error: Error: Missing translation: navigation.subnav.textReplacements at http://localhost:7357/assets/tests.js, line 12058
---
    Log: |
        { type: 'error',
          text: 'Error: Missing translation: navigation.subnav.textReplacements at http://localhost:7357/assets/tests.js, line 12058\n' }
...
not ok 67 PhantomJS 2.1 - Acceptance | language dropdown: setting a language preference persists after logout
---
    actual: >
        null
    expected: >
        null
    stack: >
        http://localhost:7357/assets/tests.js:12058
    message: >
        Error: Missing translation: navigation.subnav.textReplacements
    Log: |
...

The ember-i18n docs say that it should work fine with tests that call startApp(), which this test does. What's weird to me is that the commented-out line, when uncommented, breaks not just this test but tests in other files too. I'm guessing it's affecting some global (within the test process) i18n setting, and this setting is not getting torn down after this test finishes, but I can't be sure.

Code lives here- http://ift.tt/2wlz1Dn

The latest commit represents the failing test.