Greasy Fork is available in English.
Adds a button to toggle a dark youtube style.
Check the bottom right corner. The button hides off screen on a little tab. :)
http://i.imgur.com/tI9wD74.png
I don't see it, but I'm still gonna give a good rating since I believe you.
Where is the button to change to Dark Tube?
I can't find the button anywhere.