Yes, as noted in the disclaimer this add-on is based on that free code from Heise Online. It has been enhanced, translated and recoded for easy use with Xenforo software and even provide it's own admin option panel.
The provided dummy Facebook image says "Like". As soon as someone activates the live connection to Facebook it will switch to your language automatically.
If you would like to customize the dummy image, you can freely do so.
Just create (or edit the english one) to your liking, save it in any place at your server and adapt "Path to local Facebook share icon" in the ACP options for this add-on to the image you just created.
It does not show my language and I have set local language settings in ACP to my language. Even if I log in to my FB account and then activate share buttons it still shows in english. Sorry, really don't know what to do.