Did you catch this footnote-like message? Hopefully, by exposing this as a standalone topic it will get the exposure it deserves.
Hidden in a Microsoft blog postthat exalted the release of Windows 8.1 Preview, was a small, quick blurb about an issue with Windows RT and the Windows RT 8.1 Preview:
Please note: If you are on Windows RT and have installed a language pack, please don’t install the Windows RT 8.1 Preview at this time. A fix is coming so check back soon.
It was typed in italics making it easy to gloss over, but it's worthy of mentioning because I've seen several community members asking about Windows RT and the language packs. There's no explanation of what may happen, i.e., if it will bomb, destroy the Windows RT unit, or will simply not install, but just that a fix is coming.
Let's hope the fix is soon, communicated in a prominent style and not written in italics.
If you catch wind of the fix, let us know.