I feel like your are ignoring your customers. Please make my statement invalid by providing a reply here...

We met last Thursday and discussed about this error. They are saying, this is not a core DNN bug, so you as the developers should find out the cause and provide a solution to us (clients).

About the localization discussion, there weren't enough room to discuss it however, i checked DNN 6.0.1 and for multi-locale e.g tabs, modules... Duplication is made with custom content for each locale.
So, to localize dynamically, your method which you demonstrated in our meeting is fine in my opinion. However, for upgrades i cannot promise this will help you maintain your module easily.

So far, i had to try hundreds of workarounds to make Smith Cart module work, but i couldn't get the same effort and feedback i did provide from your team. So, I'm sorry to say that we are still waiting for addressing this bug. I think other clients facing this issue as well. At least i saw a topic and posted a msg there.