Hello, we discovered the bug mentioned in the summary. It happens only for macOS 12.3 with Version 15.4 (17613.1.17.1.6) of Safari and we saw that it is not reproducable anymore for Release 141 (Safari 15.4, WebKit 17614.1.3.8) downloaded from Safari Technology Preview. For reference see here: https://developer.mozilla.org/en-US/docs/Web/API/SpeechSynthesis/getVoices. If you need more information feel free to get in touch. Thanks in advance and kind regards, Saraphina Böttcher
*** This bug has been marked as a duplicate of bug 237584 ***