Translations hierarchy using Kotlin delegates

// AuthMessages.kt
object AuthMessages : Messages("auth") {
    object user {
        val username by messageKey()
        val password by messageKey()
        val roles by messageKey()
        val enabled by messageKey()
    }
    object action {
        val logout by messageKey()
    }
    object role {
        val users_viewing by messageKey()
        val users_editing by messageKey()
    }
}

// Messages.kt
abstract class Messages(private val rootKey: String) {
    init {
        require(rootKey.isNotEmpty()) { "Root key can't be empty." }
    }

    protected fun messageKey() = object : ReadOnlyProperty<Any, String> {
        private var messageKey: String? = null

        override fun getValue(thisRef: Any, property: KProperty<*>): String {
            var key = messageKey
            if (key == null) {
                val nodeClassName = thisRef.javaClass.name
                val nestedClassNameIndex = nodeClassName.indexOf('$')

                key = rootKey + "." + when (nestedClassNameIndex) {
                    -1 -> property.name // top level
                    else -> { // nested
                        val parentKey = nodeClassName.substring(nestedClassNameIndex + 1).replace('$', '.')
                        "$parentKey.${property.name}"
                    }
                }
                messageKey = key
            }
            return key
        }
    }
}

// auth/messages_pl.properties
auth.user.username = Login
auth.user.password = Hasło
auth.user.enabled = Włączony?
auth.user.roles = Role

auth.action.logout = Wyloguj

auth.role.users_viewing = Podgląd użytkowników
auth.role.users_editing = Edycja użytkowników

// example
button(caption = i18n[AuthMessages.action.logout])