intl.locale property should be auto-tracked

• [ x] I am on the latest ember-intl version
• [ x] I have searched the issues of this repo and believe that this is not a duplicate

Environment

• Ember Version: 3.14
• Ember CLI Version: 3.14
• Ember Intl Version: 4.2.2
• Browser(s): Chrome
• Node Version:

Steps to Reproduce

Basically I try to remove the observers from my app, and in a helper, I have something like

import { observes } from '@ember-decorators/object';
import { inject as service } from '@ember/service';
import Helper from '@ember/component/helper';

export default class FormatListHelper extends Helper {
  @service intl;

  @observes('intl.locale')
  localeChanged() {
    this.recompute();
  }

  compute([elements]) {
    if (elements.length === 1) {
      return elements[0];
    }
    return `${elements.slice(0, -1).join(', ')} ${this.intl.t('and')} ${elements.slice(-1)}`;
  }
}

after a discussion with @rwjblue I removed the observer, and if I understood well, just rewriting as this should just work:

import { inject as service } from "@ember/service";
import Helper from "@ember/component/helper";

export default class FormatListHelper extends Helper {
  @service intl;

  compute([elements]) {
    if (elements.length === 1) {
      return elements[0];
    }

    return `${elements.slice(0, -1).join(", ")} ${this.intl.t(
      "and"
    )} ${elements.slice(-1)}`;
  }
}

But for now, I have to access the intl.locale property in order to make it work:

import { inject as service } from "@ember/service";
import Helper from "@ember/component/helper";

export default class FormatListHelper extends Helper {
  @service intl;

  compute([elements]) {
    if (elements.length === 1) {
      return elements[0];
    }

    this.intl.locale; // used to force auto-tracking of `ember-intl`'s locale computed

    return `${elements.slice(0, -1).join(", ")} ${this.intl.t(
      "and"
    )} ${elements.slice(-1)}`;
  }
}

[sly7-7]

also, cc/ @marcoow, just for information

[richard-viney]

I’ve opened a PR #1340 aiming to address this issue. If anyone is able to review and/or test it out that’d be great 👍.