All parameter values are strings in Java view, viz. setValue expects a string
//UnitOfWork besorgen
IUnitOfWork uow=self.getUnitOfWOrk();
//Parameter setzen
((MechatronicObject) selectedEOs.get(0)).getParameter("Anlage").setValue("MA");
If formulas are set as paramter values, in opposite to setValue setPrettyValue should be used: Thus absolute type names become rugged against renaming the referenced classes.
//UnitOfWork besorgen
uow=self.getUnitOfWOrk();
//Parameter setzen
selectedEOs.get(0).getParameter("Anlage").setValue("MA");
selectedEOs.get(0).getParameter("Anlage").
setPrettyValue("=if existsRef('Library.Unit.Component')
then ref('Library.Unit.Component').$Anlage else 'MA' endif")