Recently I’ve made a few posts about how to support different cultures and accents when using the Windows Phone 7 Long List Selector from the Windows Phone Toolkit. So rather than try and explain each bit I decided to finally publish the code showing how the MSDN sample can be altered to support both accented groupings and cultures;
https://wp7llssample.codeplex.com/
The sample is provided as-is, the code is mostly from MSDN with a few tweaks. You should not accept this as production ready code, please carry out your own tests.
Accented grouping
Japanese grouping
Japanese Jump List
IT Bytes 
As the instigator for this post, I am very grateful for your efforts.