We do Kuma UI localization via Pontoon, but we have never resources to do localization of all the documentation on MDN. There are good reasons not to start (hard to keep few thousands technical articles up-to-date + the terminology + the audience probably want the content in English anyway). But Michal has discovered there are some, that are not necessary technical. For a start, we can make a list of typical documents on MDN (e.g. JS docs, Mozilla products/system docs, Mozilla contributors tutorial and how-tos, ...) and decide, which of them should or should not be translated.
Here is the list of MDN revisions for Czech.
We have agreed to not translate documentation for now, but only wiki-like articles (e.g. what is HMTL).
a month ago