I'd recommend to use whatever format given platform has native, otherwise you will cause you lot of extra troubles.
You can then either use some tools to convert and merge these formats (translate-toolkit is great in this) or use some translation platform which will allow you to translate all of them in one interface. Transifex (service), Crowdin (service) or Weblate (service or instalable) should be able to do this.
Weblate can help you also with keeping them in sync, I don't think others have such feature (I'm author of Weblate).