The interface should be pulling from the language setting. For this issue, I recommend opening a ticket with Customer Care for further investigation. In the ticket include the property name and an example rule where this occurs.
In General , we have an Account Setting in DTM Interface where a user choose the desired language from the drop-down list. The user interface displays in the selected language. In the upper right corner of the dynamic tag management interface, click > Account Settings and screen like below screen will be displayed. Please check whether the correct language option is selected or not.
If the correct language option has already been selected , Can you please let us know whether the label language problem exists only on the Rules section pages or on all pages of DTM Interface?.