This was found during QA for Moodle 3.5, but did not cause a specific test to fail.

I was working on a test that required switching the language to a RTL language. In Clean this large language menu displays the first 6 items, and there is scrollbar to have access to the rest of the options.

In Boost, 21 languages were displayed on my screen, making all the other choices unselectable. There is no scrollbar.