TinyMCE removes the <span lang="XX" class="multilang"> when saving.

To replicate:

1. Select Atto as your editor
2. Add a Page
3. Use the moodle tag <span lang="XX" class="multilang"> to create texts in two languages
4. Save
5. Verify that the texts changes language when you changing language in your profile
6. Select TinyMCE as your editor
7. Select to edit the page you just created
8. Save without changing anything
9. Verify that your language setting doesn't matter, now booth texts are visible