I'm recently told that ISO-10646
is now fully approved by ISO.
Is this true ?
Yes definitely. It is fully approved. It should publish early next
year (hopefully January).
Since it is more than 8-bits, is there some reason (that I haven't thought of)
why we should pick a particular convention on encoding it into 7 bits?
I don't think we need to do this last.
Although it is more than 8 bits there are several alternative.
1) UCS-2 is 16 bits and is the only part of the standard that has
any data in it. Mail that allows all 8 bit characters does not have
to do anything special except mark where the boundaries of the UCS-2
data are in the file. They are after all, just two 8 bit bytes.
2) Encode the data with UTF-1 which is mentioned in a non-normative
appendix. This prevents some of the characters that cause problems
from appearing as either of the two bytes.
3) Encode the data with UTF-2 or FSS-UTF, a different but similar
encoding that has been worked out by a joint committee of Uniforum and
X/Open. This eliminates even more problem characters, in particular
the ones that typically cause grief if used in a Unix filename.