Can you clarify, do you want to compare the source file with the translated file? Because it is clear that they will be different. So it is not 100% clear from the request what exactly you want to do.
The typical practice of checking the file content is when downloading translations from Crowdin, but not when uploading translations to Crowdin (we will not add anything).
So, when downloading translations, there is the Build Project File Translation method, where there is an opportunity to check for updates using the If-None-Match header. In other cases, it is not a big deal if you make a network request, Crowdin will skip everything that does not need to be updated.