Vanyo Georgiev posted in this Moodle forum: https://moodle.org/mod/forum/discuss.php?d=243673 , about a more flexible version of multilang filter, hosted at https://github.com/vanyog/multilangsecond:
This filter is a more flexible version of multilang filter. It has an admin setting filter_multilangsecond_mode. If this setting is set to true non html syntax can be used for multilang blocks like {mlang en}English{mlang}{mlang bg}Bulgarian{mlang} Otherwise language block is a serie of identical html tags with lang="XX" atributes: <h1 lang="en">Heading in English</h1> <h1 lang="bg">Heading in Bulgarian</h1> or <p lang="en" style="...">Paragraph in English</p> <p lang="bg" class="...">Paragraph in Bulgarian</p> <p lang="ro">Paragraph in Romanian</p> The old syntax with <lang> tags is valid too.
Please, try the filter and give him some feedback.