It's not an option yet.
Not all cultures have the same naming convention for relatives. As such Geni has not enabled translation on relative names until they figure out how to handle the differences in the naming conventions between the different cultures.
Lauri, these "half way" solutions are often HARDER to do, than the full one would be, because you have to make exceptions. Patience please. ;-) Geni has made giant steps forward in the three years I have been here.