Rails I18n: error 'translation missing' when i try translate this words "off"

Why I can't translate this word?

config/locales/pt-BR.yml

pt-BR:
  testing:
    off: 'Desligado'
    offff: 'Test'

rails console

> I18n.t 'testing.offff'
=> "Test"
> I18n.t 'testing.off'
=> "translation missing: pt-BR.testing.off"