Does anybody know, what the channel mode +C means?

I know that +c supresses color codes, but what is +C for?

depends on the network you're on
on mine C forbids cyrilic encoded nicknames to enter the channel

The +|-C channel mode prevents any CTCP's - they will be rejected.
Example:
/mode #mIRC +C
/ctcp #mIRC version
This mode is not available on all networks.

Yep, depends.. or...
C = No CTCPs allowed in the channel

Try this:

/quote help cmode, or cmodes

all I get is a list but no describtion

You can go to IRCd's website to find out, or download IRCd and check the docs.

Type /quote version for info.

best is ask tour admin network
"what is +C modes mean on Channel ???"
coz most of here is come from defferent network

like my network is hybrid
different people maybe different network

mode +C (or +c) is not defined by the official IRC protocol (RFC 1459,2810-2813). However the protocol allows addition of new modes by servers/networks.

I would suggest some networks added +C but this doesn't seem to exist on Undernet, which is the only network I know of.

The RFCs 2810-2813 are not "official IRC protocols", they're made by IRCnet for IRCnet only.