If you want to enable language fallback. Yes, below configuration needs to be set. 

It can be set in Sitecore.LanguageFallback.config or on `<site>` nodes in Sitecore.config. Both are same. 

But its recommended using patch files for any modifications.

    <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>

if you have site 2 you need to add:

    <site name="site2">
        <patch:attribute name="enableItemLanguageFallback">true</patch:attribute>
        <patch:attribute name="enableFieldLanguageFallback">true</patch:attribute>
      </site>

Here is the official sitecore documentation on language-fallback: https://doc.sitecore.net/sitecore_experience_platform/setting_up__maintaining/language_fallback/language_fallback