When you say HTML editor, do you mean the WYSIWYG-Editor in Moodle? If yes, it is most likely the source of your problems. See these discussions:
https://moodle.org/mod/forum/discuss.php?d=204180
https://moodle.org/mod/forum/discuss.php?d=257565
Lounge
Tutorial moodle 2.6 multilanguage
This discussion has been locked so you can no longer reply to it.