Webform translation while keeping single node
The method in the documentation is working:


Go to the Webform Form settings at node/1/webform/configure
Check "localization by string translation" and "Expose webform
component strings suitable for translation."
If dealing with an existing webform, then go to Go to Configuration -> Translate interface -> Strings
Enable "Webform localization" checkbox (this is important)
And Refresh Strings
Then you will be able to see the string in Configuration -> Translate interface -> Translate


At least this works for me.