I have just experienced something weird with the language filter in combination with the Google crawler.
If I switch on browser detection, Joomla returns a 404 (I assume, because no "ALL language" article is present), as the crawler has no language preference. I thought, the default language would be used in such a case.
Haven't found a solution yet, to get the same behaviour as when access is made by a visitor through a browser.
How do you handle this?