I hade a very nice experience with Android SDK and it’s features like over the air delivery, screenshots, real time preview and all other stuff.
Maybe there’s something ealse for webapp? Mine is build in Javascript mainly (this is what my developer says, I’m not a tech guy). Need just some nice tool for this localisation 
This one should work for you mate
A new tool, Crowdin OTA JS Client. It’s like a 2-3 months old, not more. From what I read about it, logic is the same to Android SDK, because both are based on over the air. This one also allows you to transfer translation, but this time to web application, and works with all or almost all web you can find. I’d say you should give it a try 