Created a MIME type but files with that extension are not registering properly

Question

I've tried following the instructions listed here and the source originally referenced in that post (7 years ago for 12.04 LTS).

I've tried...

1. Editing /etc/mime.types directly.

text/kivy-text                   kv

2. Creating the xml file in usr/share/mime/applications:

<?xml version="1.0" encoding="UTF-8"?>
<mime-type xmlns='http://www.freedesktop.org/standards/shared-mime-info' type="text/kivy-text">
  <comment>Kivylang text file</comment>
  <glob pattern="*.kv"/>
</mime-type>

3. Creating the xml file in user/share/mime/packages:

<?xml version="1.0" encoding="UTF-8"?>
<mime-info xmlns='http://www.freedesktop.org/standards/shared-mime-info'>
  <mime-type type="text/kivy-text">
    <comment>Kivylang text file</comment>
    <glob pattern="*.kv"/>
  </mime-type>
</mime-info>

In each case I tried following up with:

sudo update-mime-database /usr/share/mime

A comment in the above thread mentions that adding the file in applications causes the file to be deleted when running the command above. This was my experience as well.

Running it after creating the file usr/share/mime/packages created a successful entry in /etc/mime.types and another file in user/share/mime/text but .kv files still show as text/plain text in Nautilus.

Edit: I thought rebooting might help as well. It did not.