What is the reason old pages are still indexed?

[jetchen]

I have a domain has been used to show Chinese content, but now it is used to show English content, but I found Googlebot like index the pages which contains chinese content,What is the reason£¿

[piatkow]

Do the pages still exist?
Removing links to pages doesn't stop the googlebot once it knows about a page.

If the pages are spidered infrequently they may hang around in the index for a long time. I don't know what it takes for G to recognise that a 404 error is permanent but as a webmaster I hope there is some leeway to cope with temporary glitches.

[g1smd]

It takes months for old URLs to drop out of the index.

While they still rank they can still bring traffic.

[TheMadScientist]

404 error is permanent

A 410 is permanent.

A 404 is not necessarily permanent...
A 404 is an 'unknown situation' which may or may not be permanent.

[404 - Not Found] The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.

[410 - Gone] The requested resource is no longer available at the server and no forwarding address is known. This condition is expected to be considered permanent.

HTTP 1.1 Status Code Definitions [w3.org]