In your config/locales folder, create an activerecord.nl.yml (e.g. for Dutch), then in that file put the active record translations as follows
nl:
activerecord:
models:
coupon: translation
coupons: translation
As for the labels and buttons, create a simple-form.nl.yml file, containing
nl:
buttons: &buttons
submit: translation
...
and
labels: &labels
name: translation
...
at the end of that file, put
simple_form:
buttons:
defaults:
<<: *buttons
labels:
defaults:
<<: *labels
by splitting up the list of labels and buttons from the simple form section, you can also use them elsewhere in your views