When it happens, are you logged in with a user who may be using a different language than your default? This can be set using some different extensions.
Also, when it happens randomly, is it always on the same page when it does happen, or does it happen on different pages? Can you post a link to your site so we can see how it looks? Finally, if there's anything we should do to help our chances of recreating it, let us know.
Thanks!