Href lang only on the translated pages or also on the main language pages?

I’m in the process of duplicating all my pages in webflow. Now I was wondering do I need to put the alternate hreflang only on the translated pages or also on the original language pages?

Example of such a tag:

<link rel="alternate" hreflang="en" href="http://www.mywebsite.com">

Oh @webflow just freaking build a webflow translation tool, but that frustration is for an other topic :wink: