About [[MediaWiki:Gwtoolset-multiple-files/en]]
Fragment of a discussion from Translating talk:MediaWiki
You are right, this message is poorly written. I expanded the documentation, I hope it makes sense now.
We understand what the descried situatiion is, but the message text makes less sense than ever and needs to be redone. Only one file can be submitted at a time. is apparently outright wrong, according to the current message documentation, which states that two files had been uploaded.