Firstly, this is for High Sierra
I've already tried this step:
Add a second language like French in Settings -> Keyboard -> Input Source
When I type
defaults read -g ApplePressAndHoldEnabledin a Terminal I got a
- Go into Settings, Keyboard and make sure the Key Repeat slider is set to Slow and the Delay Until Repeat slider is set to Short.
Even if I restart the Accent Menu doesn't appear.
And this is my Mac:
macOS High Sierra | version 10.13, MacBook Pro (Retina, 15-inch, Mid 2015)