Which charset should el_GR@euro be using?

[Petter Reinholdtsen]

What is the correct charset for the locale el_GR@euro.  The el_GR
locale uses ISO-8859-7, but it is missing the EURO SIGN.  The EURO
SIGN is present in ISO-8859-15, but the current el_GR@euro locale do
not build with ISO-8859-15.  It gives "unknown character in field" for
yesexpr, noexpr, abday, day, abmon and mon (as expected).  There is no
author listed for the el_GR@euro locale, so I do not know who to ask.
Anyone know which charset it should use?