According to the documentation, I should be able to provide translated screenshots using the xml:lang attribute. I have the following example file:

<?xml version='1.0' encoding='utf-8'?>
<component type="desktop">
  <id>org.example.App</id>
  <name>Test</name>
  <summary>Test</summary>
  <screenshots>
    <screenshot type="default">
      <image type="source">https://upload.wikimedia.org/wikipedia/commons/c/ce/PNG_demo_Banana.png</image>
      <image type="source" xml:lang="de">https://upload.wikimedia.org/wikipedia/commons/3/39/PNG_demo_heatmap_Banana.png</image>
    </screenshot>
  </screenshots>
  <content_rating type="oars-1.1"/>
</component>

This is a little examples which contains just 2 images from Wikipedia for testing reasons.

If I view it with:

gnome-software --show-metainfo=org.example.App.metainfo.xml

As I have A German System, I see the second Image.

Now I try to view it in English:

LC_ALL=C gnome-software --show-metainfo=org.example.App.metainfo.xml

The User interface of Gnome Software is now in English, but I still see the second Image, which is ,marked as the German translation. Is this a Bug in Gnome Software or is just the Documentation wrong?