It does not happen often, but it really bothers me when I get chinese page results (especially with google image search where I can't tell that it's chinese until I click on it).

Is there any way to block chinese language pages? It should not be that hard to detect, you can usually realize it within seconds, surely there must be a addon or something.

The quick & dirty way is to just put a は　or が　in your query. Not sure if there's something more technological.

Options -> Advanced search -> "Then narrow your results by" language -> Japanese

Doesn't work for image search, but there you can narrow results by region (Japan) or by site/domain (.jp)

Searching on google.co.jp does the trick for me.

<bragging mode="shameless">I made this suggestion to the Tangorin guy a while back & he added a link for it.</bragging>

I just add "jp" to any term I'm searching, when I want the results from JP sites only, usually it is enough. Add "site:jp" when you want to restrict even more.