How to use interface locale-control

I added the locale-control plug to my snap:

apps:
  my-app:
    command: usr/bin/app
    plugs:
      - locale-control

But get this error:

$ snap run --shell app.my-app
$ localectl 
bash: /usr/bin/localectl: Permission denied
$ locale --all-locales
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_COLLATE to default locale: No such file or directory
C
C.UTF-8
POSIX

On the host

$ localectl 
   System Locale: LANG=en_US.UTF-8
       VC Keymap: us
      X11 Layout: us,de
       X11 Model: pc105
     X11 Variant: ,
     X11 Options: grp_led:scroll
$ locale --all-locales
C
C.utf8
en_US.utf8
POSIX

I was expecting that the snap would have access to the en_US.utf8 locale and that I would be able to switch locales from the snap.

What am I missing?