My first thougth was : who says that there are utf8 chars in the map?

Ahhh. You said that --utf8 was no option. But I had to read it as : use --charset=utf8
So mkgmap can make those .img’s. Nice, I hope it just transfers the text untouched.

Well actually it does. That looks exactly like the chars in the transliteration table for greece that I use. See here some characters (copied from wordpad): look at tke leftmost column.

Λ=Ë=L
έ=å=e
ν=í=n
Ï„=ô=t
α=á=a
Ï‚=ò=s
é=e=e
Δ=Ä=D
μ=ì=m
Τ=Ô=T

And the same displayed by firefox and copied from it.
Λ=�=L
έ=�=e
ν=�=n
τ=�=t
α=�=a
ς=�=s
é=e=e
Δ=�=D

The Nuvi displays utf8 with a normal ansi charset (for one byte chars). On the nuvi screen there are 28 character. Those are 14 utf8 characters. Using my transliterationtable i come to Mikala… And looking at openstreetmap http://www.openstreetmap.org/?mlat=37.9761725887055&mlon=23.7486863136292&zoom=16&layers=B000FTF that is right.