Can I use multiple languages in my metadata description?

Yes. If you tick the checkmark next to Multilingual for an element in the Component Registry, it will result in a multilingual field. With the xml:lang attribute you can then indicate the language in which an element has been described, see eg. the following fragment in this example CMDI file:

<!-- Note the support for multilingual fields, using the xml:lang attribute -->
<title xml:lang="eng">mister</title>
<title xml:lang="fra">monsieur</title>
<title xml:lang="nld">mijnheer</title>

For indicating the language we strongly advice to use the ISO-639-3 language code.

Please note that enabling Multilingual will make the element repeatable, even if the Maximum number of occurences is set to 1.