If I try that directly, I'm redirected to the Ubuntu.com landing page... if I remove the lang= parameter, I get release notes.
When I was doing install testing and noticed this, I was using the Desktop isos as of 4/13. For language at the beginning, I chose the default of English in the Language Selection that pops up as soon as the ISO boots.
Also, I was booting the ISO as a CD device in a VirtualBox VM.
I also just tried this using the i386 DVD from yesterday and got the same result. Also of note: when Firefox opens when I click on the Release Notes link, I get the popup that tells me that FF is not the default browser.