Does the forum logs give an error when it crashes?
Do you have mongo and nginx logs on?
There should be some useful information in one of the logs as to what is happening.
When I change language in admin settings and restart server, application is still in old language ...
On master with last commit :
2e49fe9 2014-05-18 | fixed meta property to name, for keywords (HEAD, origin/master, origin/HEAD, master) [Julian Lam]
It works for me on latest. Maybe try to clear your cache.
@dove it is working.