For months I was annoyed by the language in my GUI (on Windows XP) not conforming to settings.
In one case, the solution is to set the LANG variable in Windows:
1. Right-click My Computer, and then click Properties.
2. Click the Advanced tab > Environment variables
3. Click New to add a new system variable with name “LANG” and value “fr_CH” for example (Swiss french).
Also set 'lang = fr_CH' in the client section of c:\Documents and Settings\USERNAME\.openerprc
(however in v5.0.6 this keeps getting written back to en_US: setting the file to read-only stops that, but the etting is still not used correctly).
On the server side, make sure there is a corresponding entry under Administration -> Translation -> Application Terms -> Languages.
I must admit that despite the above a v5.0.6 instance on mine still puts all dates in American format, with Menu lang in french.
So date formatting is broken, in v5.0.6 at least.