How do Ign and Hit affect apt-get update?

My understanding of Ign and Hit which are displayed in the output of the command apt-get update is that Hit: File found. No change in its timestamp and Ign: File ignored. No change in its content..

What does this mean exactly? For example if a package is to be upgraded does it mean that its timestamp has changed as has its contents?

From what I can see in the apt source code, "Ign" means there was an error retrieving the file, but the error is being ignored. When I run apt-get update, I see 3 Ign messages, all of which are for Translation-en files. A packet dump shows that the requests for those files got HTTP 404 responses.

So the translation files are missing, which makes sense because we don't need a translation of the package database from English into English, and apt doesn't consider the lack of translations to be a fatal error. (Even on systems configured for some other language, the lack of translations wouldn't be a fatal error, it would just mean that you'd be forced to read package descriptions in the default language instead of your local preferred language.)

"Hit" on the other hand means exactly what you said. The file was found on the server and it hasn't been changed since the last time it was downloaded. This is indicated by HTTP code 304. Note that we're not talking about timestamps on individual packages, sinceapt-get update doesn't download those. It downloads the list of available packages and other related information. The timestamps being compared are on those list files, not the packages themselves.