See MDL-7437.

We still need to:

1) Add a routine in the upgrade to convert old multilang tags to the new method:

<span lang="fr">Bonjour!</span> and <lang lang="fr">Bonjour!</lang>

to:

<span lang="fr" class="multilang">Bonjour!</span>

2) Modify the multilang filter to look for the new classes, and optionally to support the old tags as well (filter config setting).

I know these will be easy for you!