2 wordpress, 1 database



Are you using different versions for different languages by any chance? If so, check out the qTranslate plugin and save yourself from the trouble.

Otherwise, check out this guy's instructions: Sharing one database between two wordpress installations.
It has it's downfalls like not being able to log in to the second installation by using the default administrator login but you can workaround it.

I've tried this trick with one site where i needed more versions of the site for more language variations, but opted for that language plugin instead.