In a multi-language solution all the Sitecore items have different versions in different languages. Depending on your configuration, you can load the items by adding a language parameter in the url, e.g.:

English: http://mysite/en/myitem
German: http://mysite/de/myitem

Now what happens when myitem only has a language version in English, but not in German? Right, this usually should result in a 404 (page not found) error message. But it doesn’t out-of-the-box. Check the following code:

var language = Sitecore.Context.Language; // = de
var item = Sitecore.Context.Database.GetItem("<id>", language);
var itemIsNull = item == null; // = false

This means, Sitecore always returns an item, also when there is no language version available. The item is called an empty item. Empty items contains either empty values or Sitecore macros, like $name. My blog post about Provoke 404 for inexistent language version show you how you can ensure that a language version exist.

In Sitecore 8.1, one of the new features is that you can configure if Sitecore should return an empty item for inexistent language versions or if it should return null. By default, this is disabled and everything works as it worked before. To enable the feature, you need to set the property enforceVersionPresence="true" in all your <sites>-configuration, including the shell site. After doing this, you also need to enable it on all your items where you want to have this enabled. I recommend doing this on the standard values of your data templates. You can do this by activating the Standard Fields and then enable the checkbox for Enforce Version Presence in the section Advanced:

enforce version presence

Voila. If you want to disable this check for a particular code-snippet, you can use the EnforceVersionPresenceDisabler to temporary disable it:

using (new EnforceVersionPresenceDisabler())
    // Should now always return an item instance
    var item = Sitecore.Context.Database.GetItem("<id>");

A last hint: When you work with Glass Mapper and load items over it, Glass Mapper already checks if there is a valid language version available and return null if not. But you should still enable this setting, because Sitecore internally doesn’t use Glass Mapper, so you would still need to provoke the 404-page on your own.

For all my feature projects, this will definitely be default config. Hope this helps you too to get rid of some code for validating language versions. The official documentation on this feature can also be found on Sitecore docs.