Hi, I know that you don't provide the translation, but that is not the issue here.
When I login on Joomla in backend in Dutch-NL, the whole Joomla site is in Dutch, except for jomsocial, that part is in english. In the past, my Dutch translation of backend was ok, worked normally.
I downloaded again the language pack after you updated the package. I Installed it again. On the server I can see it's correctly put in ..\joomla\administrator\language and when I open a ini-file, it's the correct one (in Dutch).
But Jomsocial refuses to read the nl-NL directory in that path, so I think this must be a bug or misconfiguration, because language files are ok.