Text to speech voice

I'm having the same experience--the default system voice selected in Accessibility -> Speech is ignored by the right-click Speech menu, and I get the default (Alex, I think).

Here's a workaround, at least: Go to Accessibility -> Speech and select your preferred language, then enable the "Speak selected text when the key is pressed" option and set a preferred key combo (default is Option-esc). This will use the correct System Voice you've selected, so you can, for example, get the vastly improved Siri to read stuff to you.

This is demonstrably a bug, at least on 10.15.7, since I could replicate it from a fresh user account and the Apple Help document explaining how to change the voice says that the Speech item from right clicking or the Edit menu should use the System voice:

https://support.apple.com/en-afri/guide/mac-help/mchlp2290/mac

Just to add, this bug still isn't fixed in Big Sur, at least as of vision 11.0.1.

Interestingly, at least in Big Sur, you can select any non-Siri voice; the bug is actually that if you select Siri you instead get the default MacInTalk voice for that language. In the case of English, it's Bruce, which isn't even one of the best ones. If you select any non-Siri voce, it works as expected. If you pick Siri in a different English accent (Irish or British, for example), you instead get the default old-style voice for that dialect.

My assumption is that Siri uses a different subsystem, and Speech menu item isn't properly tied in to it so uses the fallback.