The narrator does not narrate the word "Experimental" in the world selection screen

To reproduce:
Enable the narrator (which can be enabled by Ctrl+B), and make sure you have a world with "Experimental" enabled.
Select but don't open that world.
The screen may show the following text (for example):
Creative Mode, Cheats, Experimental, Version: xxxx
But the narrator only says:
Creative Mode, Cheats, Version: xxxx
The word "Experimental" is not said.