Show language name instead of langcode

Problem/Motivation

langcodes are internal names that should'nt be shown to final users in order to avoid confusion.

Steps to reproduce

At /admin/reports/xray-audit/number-term-type-lang and other similar reports, 'und', 'es', 'en', or even 'zxx' is shown.

Proposed resolution

Use language name instead of langcode.

Remaining tasks

MR

User interface changes

Show language names instead of langcodes.

API changes

None.

Data model changes

None.