Ember's handlebars helpers don't like having too many arguments (it allows you to have one argument and an options hash). It also doesn't like nested calls, such as having one helper that takes the result of another helper as an argument.
A while ago, we added a helper method for i18n-js that allows us to translate things in the view layer. In order to make the helper method handle string interpolation with nested translations (for example: translating "If you want to learn more, click #{here}", and then here is itself a translated link to somewhere), we make the translate helper recognize a special suffix. We called it Key, so any translation key that ends in Key represents a nested translation (such as hereKey for the earlier example).
Then, we translate the key before passing it in for string interpolation as part of the original translation.
The final method looks like this:
We also had some trouble using the message field in ember-validations, as it overwrites i18n and appeared to be setting the message value before we set our i18n-js locale, causing all our error messages to be stuck in english.
We fixed it by changing the message from trying to translate the string to just returning the translation key and changing the view accordingly to handle the translation there instead.