Manding languages
The code man is a macrolanguage for a subgroup of Manding (a sub-sub-group of Mande, if you will, including several varieties of Mandinka & Maninka). There is no ISO 639 code for the entire group of Manding languages (covering man + others like bm, dyu, and kao'). The lack of a relevant ISO 639 code shouldn't IMO prevent addition of this category (even if that might not fit conveniently with the cat boiler system (as I understand it).
Metaknowledge, thanks. Will follow up on discussion page there.
Rua, wrt valid code, I think there are some instances where departing from that convention would be useful, tho obviously not without sufficient justification for such exceptions. One of those, I would contend, is "Manding" (of which Mandingo "man" is a subset), and this assertion is based not only on linguistics but also the way this set of languages (or varieties of a language) are perceived by at least a large number of its speakers. A topic for further discussion elsewhere, of course, but please undderstand that my initial edits in this regard were not lightly considered.
Everything on Wiktionary relies on thing having a code, whether it's for a language or a family. So there is really no way to depart from that convention without breaking everything, and having a code to use is a requirement for being able to do anything regarding a family or language. For example, the categories for language families are created with {{famcatboiler}}, which requires a code as the first parameter. So without the code, there can't be a category either.
That said, Wiktionary creates its own codes when there isn't one available in ISO 639. So if there is no code available for something, a new one can be created and added to our database. The database can only be edited by administrators, so you can request one at WT:GP and someone will do it for you. The reason I didn't do it myself is, as I mentioned, that I didn't know anything about these languages and I was confused by the fact that Wikipedia said man was the code for this family, while we already use that code for a specific language. Metaknowledge knows more about these languages, so he was able to judge it correct and added a code for you (along with some unnecessarily snide remarks towards me, just for trying to be cautious). In any case, for more information, you may find WT:Languages and WT:Families useful.