The dialog configuration fields saveLabel and cancelLabel cannot be internationalized.
While all other dialog labels (for controls, tabs. etc...) can be internationalized, cancelLabel and saveLabel cannot.
They use either the configured value directly, or if no value is configured, they use the default label (which is i18n).
This should be changed to allow i18n for these labels. A patch is attached.
See info.magnolia.cms.gui.dialog.Dialog.java, lines 260 and 270.