How to reproduce

1. Log into the latest Moodle sandbox as an admin or teacher
2. Go to a course
3. Turn on edit mode
4. Add an activity
5. Inspect the markup for the "All" tab

Findings

The aria-label for the "All" tab is "Default activities" instead of "All" or "All activities". 

Accessible name not containing the visible name is a failure of WCAG SC 2.5.3: Label in name (Level A).

Users who navigate the page using speech input may have trouble selecting the tab as they will be using the visual label to trigger speech activation but this doesn't match the label exposed to assistive technology.

Suggested approach

The accessible label should match or start with the text in the visible label, for example "All" or "All activities".