In Goldendict, hotkey Alt-s is useful to pronounce current word. And I set mpv as the external program. But after I configure mpv with much custom tweak and plugins, this keybinding no longer work. Maybe some configurations make Goldendict can not invoke mpv to play audio.
Finally, I find a simple way to fix it. There is no need to set up mpv to compatible with Goldendict. Using
mpv --no-config as the external program will use a pure mpv without any custom configuration. And Goldendict will invoke a vanilla mpv for the audio playback.