This is an excellent point, which I will bring up with my tech lead.
I spoke to my tech lead, and he said:
- You're right.
- The reason we have OK/Cancel is we're using the default dialog window.
- This message is not frequently seen.
For now, I will rephrase the English-language message to make it clearer what the user should do. It may take a few days for the change to show up in translatewiki.