using applescript to set a system voice

Provided you have granted Script Editor access under Accessibility, this snippet will let you set a system voice. Edit Moira (Enhanced) to your preference.

tell application "System Settings"
    activate
    -- set moira as the system voice
    delay 1
    reveal anchor "AX_SPOKEN_VOICE" of pane id "com.apple.Accessibility-Settings.extension"
    delay 1
    tell application "System Events"
        click pop up button 2 of group 1 of scroll area 1 of group 1 of group 2 of splitter group 1 of group 1 of window "Spoken Content" of application process "System Settings"
        delay 0.75
        click menu item "Moira (Enhanced)" of menu 1 of pop up button 2 of group 1 of scroll area 1 of group 1 of group 2 of splitter group 1 of group 1 of window "Spoken Content" of application process "System Settings"
    end tell
    close
end tell