The only thing that should be using env() is your config files. If you cache the config, which you should do in production, it will ignore env totally and only pull values from config.
but for one thing, it's locale in your config (lowercase), but you're trying to reference it with LOCALE uppercase.
Thanks, but even with 'locale' instead of 'LOCALE'
on the "AppServiceProvider" boot method don't translates. With that "Carbon::setLocale(config('app.locale'));" the 'de' needs to be put where?