xedoc.Element("artikel").Element("inhalt").Element("text").Add(new XElement("absatz"));
xedoc.Element("artikel").Element("inhalt").Element("text").Element("absatz").Add(paragraphvalue);
You create a new
absatz
element, but you are not using its reference to add the paragraph item. The second line will add the item to the first element that it finds with the name
absatz
.