There is no special support for something like this in yEd. However, you could try to use custom properties to manage multiple languages. E.g. for each node create a text property "label.text.de" for German label text and "label.text.en" for English label text. After specifying the appropriate German and English texts for each node, you can use the properties mapper to set the nodes' actual labels to either the German or the English text.
See Mapping Custom Properties to Visual Properties for additional information on custom properties and properties mapper.
