Rails I18n nested translation keys

I'm not going to answer your question (I don't think it's possible with the i18n gem but could be wrong). I am going to say that you shouldn't take this approach and give you link [1] as background. As developers it's natural to see patterns and extract common code to keep things DRY. This is a step too far when dealing with multiple languages as it prevents proper translations. Not all languages follow the same sentence structure as english and what you're substituting in may have to change to agree with the rest of the sentence.

On a site I work on we have this problem with French. We have sentences that include a location name and this is straightforward in English. "%{location_name} property" works whatever the location name is. In French however, you need different structures depending on whether the location is a town, a province, a region, and whether the name starts with a vowel or not.

[1] http://www.multilingual.com/articleDetail.php?id=594