Hello,
as described in another question (http://plantuml.sourceforge.net/qa/?qa=4637/is-there-a-way-to-control-the-box-minimum-size-width), one can use the skinparam minClassWidth to change the minimum width of classes.
But I was not able to find this skinparam in java -jar plantuml.jar -language, the set of words of the plantuml language. What is the reason for this?