The text rendering works correctly for Label and TextButton texts, but is broken for:
Tooltips (hover over the middle button, the tooltip shows strange symbols)
ThreadWithProgressWindow title. For some reason its ProgressBar and Cancel button render correctly, though.
The Slider popup text renders correctly.
And there’s a crash: If you hover over the Slider (don’t click it) and quit the app (using ⌘Q) while the popup is still showing, it crashes in ~PopupDisplayComponent().
Can you upload a screenshot of the strange symbols? There has been a similar issue a few weeks ago that has been patched on some versions of OS X, but not 10.13.6.
See this thread that lead to a patch which lead to garbled text for some people: