What is the use of "shell" website in the Sitecore.LanguageFallback.config file

Question

If I don't include <site name="shell">, what impact will it have?

Answer 1

Shell website is a Sitecore site used by Sitecore backend.

 <!-- ENABLE ITEM AND LANGUAGE FALLBACK PER SITE
         Using attribute patching below you can pick which fallback mode to enable (item-level or field-level or both) for each site 
         Consult official documentation on how to enable fallback feature in complex multi-site environments.
    -->
    <sites>
      <site name="shell">
        <patch:attribute name="enableItemLanguageFallback">false</patch:attribute>
        <patch:attribute name="enableFieldLanguageFallback">false</patch:attribute>
      </site>
    </sites>

On Sitecore.LanguageFallback.config you have this config that tell you FieldLanguageFallback and ItemLanguageFallback is disabled.

To be able to use language fallback in your Sitecore solution, you have to enable it for each relevant site.

To enable site-level language fallback:

Open \Website\App_Config\Include\Sitecore.LanguageFallback.config and set the following attributes to true: enableItemLanguageFallback and enableFieldLanguageFallback

You must enable the attributes on the shell and on each of the relevant websites.

<sites>
      <site name="shell">
        <patch:attribute name="enableItemLanguageFallback">true</patch:attribute>
        <patch:attribute name="enableFieldLanguageFallback">true</patch:attribute>
      </site>
      <site name="website">
        <patch:attribute name="enableItemLanguageFallback">true</patch:attribute>
        <patch:attribute name="enableFieldLanguageFallback">true</patch:attribute>
      </site>
</sites>

In multisite environments where you only want to enable language fallback on a subset of the websites, you need to create a specific shell site for each website where you want the language fallback feature enabled.

More informations about language fallback you can find here: https://doc.sitecore.net/sitecore_experience_platform/setting_up_and_maintaining/language_fallback