Are you using a localization target name other than “Game”? We discovered that the cooking/staging logic currently is hard coded to cook/stage only the “Game” target, not others. That issue is filed as Jira ticket UE-20248 currently.
Note: The translations for text in these maps is not located in the maps, but in the binary locres file for the localization target containing the text gathered from those maps. This means that the translations will be present, regardless of the map being downloaded on the fly. It is possible to download the binary locres files separately and load them up as necessary - if this is necessary, we can help you with that.