Amenities not included in Language Manager of Joomla Real Estate Component, you can add any Amenities in any language, and then assign them on house you need. You can create any new category in any language. So, this is much better than include them in Language Manager.
You need only add Amenities (Garden, Yard, Heating, etc.) in Greek and Russian, just write them in that languages in Real Estate Manager : Amenities Manager.