Default language

Yes it is.
The first possibility is to set the browser directly to the target language.
The second one is to create a user to whom you assign the corresponding language.
You can also use a timer. Set the timer to any interval. Here it is important to set the "Elapsed Immediately" and "TimerEnabled" properties to "true". You can add two actions to the timer via the "Elapsed" action. See appendices

All three ways will change the user texts to the desired language. 

So far there is no way to do this via javasript. We put this on our workroad and it will come as a new feature.