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

<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>

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