I just found a major problem between iCal, ZCS, Mail and non-ASCII chars. First I created an event in a local calendar with the following subject :

And I invited my ZCS account and sent out the invitation. The invitation subject is ok when I view it in ZCS Web client :

But things go ugly after I accept the invitation. The answer look like this :

And in the calendar, the event look like this :

So it look like ZCS can't deal with non-ASCII chars in events. One thing I did notice, Mail and iCal seems to use Windows-Latin-1 as the encoding for the invitation :

Subject: =?WINDOWS-1252?Q?_Tes?=
X-Mail-Calendar-Part: Yes
Date: Tue, 14 Oct 2008 10:41:26 -0400
X-Mailer: Apple Mail (2.929.2)

Content-Type: text/plain;
Content-Transfer-Encoding: quoted-printable

But ZCS reply is done in UTF-8 :

Subject: =?utf-8?Q?Accepter:_Test_a?= =?utf-8?Q?ccents_=EF=BF=BD?=
MIME-Version: 1.0
Content-Type: multipart/alternative;
X-Originating-IP: [xxx.xxx.xxx.xxx]
X-Mailer: Zimbra 5.0.9_GA_2533.RHEL5_64 (ZimbraWebClient - SAF3 (Mac)/5.0.9_GA_2533.RHEL5_64)

Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

Sujet=C2=A0: Test accents =EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=
Organisateur: probert@os.ca=20

Heure: Mardi 14 Octobre 2008, 13:45:00 - 14:45:00 (GMT-0500) America/Montre=
Invit=C3=A9s: "Pascal Robert" <probert@macti.ca>; "probert" <probert@os.ca>=


Oui, je serai pr=C3=A9sent.

Content-Type: text/html; charset=utf-8

I guess that's part of the problem?