we are developing a platform at https://translate.foe-services.de for "Social Translation". It is still in development (you can contribute at GitHub, just have a look) but stable enough for production.
I would love to set up NextGEN Gallery as a project on the platform - As soon as the functions are implemented you will get full access to your project.
If you would like to help promote it you could add a link to the plugin description.
Just get in contact here via the post or look here at GitHub: https://github.com/cfoellmann Thats me and my contact info