OpenStreetMap

You’re right about keeping the names short and simple (in this case, the A6 should just be Αττική Οδός/Attiki Odos) - however, tunnels have their own names, so in tunnels the main road name goes to the alt_name=* tag.

Another thing of interest, name:el=* is not necessary, since Greek is the official language anyway. Tempting, I know. ;-)

Sure tunnels have their own names but they are a subpart of the road! So these names should be written in alternative name.
I suppose that we should keep the row of the main name of the road.If I point on this part of map i should read the road name and not the subpart (the tunnel}.
About the name:el, I keep on using it, because I can't know which tags are used by each program. I tried to make it compatible.
About the names of highways, I also try to make then compatible.
Although we, the Greeks, don't use the numbers of the motorways, I think that the numbers are the most compatible way to print the name. it is easier for the visitors of my countriy to plan their routes using numbers than a difficult Greek name like: Nea Ethniki Odos Athinon - Thessalonikis - Evzonon. But unfortunately Greeks uses names and not numbers. What would you suggest?

* I think that the numbers are the most compatible way to print the name on the map.

Here is my reply: https://forum.openstreetmap.org/viewtopic.php?id=63677

I think it is better to discuss in the forum since it is easier to reference the posts later.