So as we thought... our developers has confirmed that this behavior is by design. Localization macros are always resolved according to the default culture.
Recipients culture is not taken into account. You can use the workaround mentioned in your first email.
On the other hand, if you want functionality like this available in the feature version of Kentico, you can suggest it and also other users will be able to vote for it (more users = higher priority), on the special page: http://kentico.uservoice.com/
Senior Support Engineer