The translation of Media Variables either happens in the Media Editor or in PARTproject.
Media Editor:
Below select the variable to be edited, top right, in the list field, set the desired language and then click on Edit.
-> Now the variable's content is shown.
PARTproject:
In the PARTtemplateDesigner, in the settings dialog Template, click on the button Open in PARTproject.
Details on this can be found under ???.