I think I recall seeing some Boglehead people claiming the intl' bond funds would be hedged so it would eliminate the currency diversification if that is the case - for better or worse.
To answer your question - I just say it depends on how much slicing and dicing you want to do & how much rebalancing you want to do each yr. As people around here have shown, you can get by with a very simple allocation that doesn't include foreign bonds.
On a side note if you are a timer + slicer/dicer with bonds, Rob Arnott's top allocation move for '12 is emerging mkt bonds. He claimed that the emerging country bonds were being dragged down by the bad news in Europe w/o justification & offer attractive returns. He's a pretty smart guy.