There are some reports in the Google Web Search Help forums of searchers seeing mixed languages in the search results. If they search for one query, they may see English but if they search for a different query, they may see a completely different language.
One searcher posted screen shots and examples saying "when I search for "potassium", the result shown would be displayed in US English, which is the default language I selected. However if I search for "beryllium", for some reason the result is instead displayed in Malay, which is the native language of my country Malaysia."
The issue seems to be tied to specific Google accounts and is not seen by all searchers.
Google has not yet responded to the issue but it seems to have been happening since Monday.
A Top Contributor named bluequoll said "Some other users have reported that Going into Search Settings and changing the Region to a specific country helps, rather than leaving it set a "Current region". That may be a useful workaround while Google is sorting this out."
Forum discussion at Google Web Search Help.