Thanks, yes, using each files' unique ID as fie name works.
However, could you take it as a feature request - please allow updating translations with their initial names a la translate_(langgroupID)_(locale).json because the current flow does not scale well without extra scripting.
Translation often takes place in some sort of CAT tool, that can easily export filenames with a certain pattern like above but usually does not support assigning unique names for every single file. Plus you really wouldn't want to do it if you have like 10 files in 10 languages... 