Hello, I live in the US but I visit the Czech Republic quite often, since I have family ties to this zoo. Couple of months in, the langurs are doing well. At the beginning, there were issues with one of the females being smaller than the others, as she was generally weak and the male was stealing her food. However, by now there are no issues anymore.
In Prague, there's a significant Vietnamese community that is supportive. Twice a week they deliver fresh leafs imported from Vietnam, so there are no problems with feeding. In case of outage, it was found that the best local alternative are raspberry leafs.
There's much that can be said about the challenges that come with keeping this species, particularly in regards to nutrition. We've received much help from zookeepers from Thailand and Philadelphia who were all most helpful. I've read all the scholarly info available and now there's a lot of own experience from this zoo. I'd be happy to share all the knowledge obtained. Not sure if this is the best platform, but if anyone is interested, feel free to contact me.
I don't read this forum often, but will try to check it here and answer any questions.
Here's a selfie I took