As part of our ongoing to #12420 renaming of everything from Piwik to Matomo, the next most important step is that our JS Tracking code should reference matomo.js and matomo.php instead of piwik.js|php. This remaining use of "Piwik" seems to be the last highly visible mention left in the product.

Suggested steps:

• The tracking code in Administration > Tracking code should reference matomo.js|php
• The API output for SitesManager.getJavascriptTag and others like SitesManager.getImageTrackingCode should also reference matomo.js|php
• it's very important that we keep backward compatibility, so the file "piwik.js" should still be there and be a copy of matomo.js file (we will need to update instructions on how to build the compiled matomo.js in https://github.com/matomo-org/matomo/blob/master/js/README.md#deployment
• And add a ReleaseChecklist test that the matomo.js is the same as piwik.js
• Search and check/replace all occurences of piwik.js in the codebase (there are many)
• Ideally we also rename the CustomPiwikJs plugin to CustomMatomoJs or CustomTrackerJs
• Possibly other steps I missed