Feature summary:

The system message at mw-changecontentmodel-success-text is displayed after a user has changed the content model of a page.

It says (by default):

The content type of [[:$1]] has been changed.

What should happen?

It should be changed to:

> The content model of [[:$1]] has been changed from $2 to $3.

1. It's content model, not content type
2. where $2 is the name of the old content model.
3. where $3 is the name of the new content model that's applied to the page.

So $2 and $3 need to be specified and passed in code.

Bonus:

There is also a grammar error in mw-changecontentmodel-success-title which says:

The content model was changed

but would be better as:

Content model changed

to simplify things.