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Main idea behind this was problem with synchronizing big volumes of translations in quasi-mature apps. Production env downloaded thousands of keys, in my opinion without much need - in most use cases production app will be released with most current translations exported from staging env. That's why it will be much easier to only synchronize (from the beginning) only changed keys, not all of them.
Also - I wanted to do it via paging, etc, but this would involve introducing some kind of background job processor as dependency - this could be made modular, etc, but I think it would be an overkill.