Why is Mansi listed with language code, but Mari with full name in macOS?

[snomos]

In the language list in the left column of the keyboard selection pane. Cf the following screen shots:

Mansi:

Mari:

Is there anything in the bundle we can provide to fix this, or is it due to limitations or missing data in macOS? If is is due to macOS, how can we document or get to know which languages are not supported by its real name?