I think, support for all languages or one language. I'm trying to compress with FreeArc with all languages. Only Data folder with all languages (16.6 GB). Compression time: ~ 2 hours.

I still don't know the final size of this data.cab. But it will be useless, just to test it. I'll have to split into several Data.cab 's or easy way: internal compression.
Maybe, 2xDVD5 will be possible with peterf1999's method, but this is out of my knowledge.
EDIT...
as REVO said, I think it will not fit on 2xDVD5.