I am wondering if there is a reason to have two traditional chinese translation.
But couldn't we have all three "zh", "zh_Hans", and "zh_Hant" in the themes?

The second commit is fine. The "X-Language-name" is an extension and not part of the standard header. Weblate preserves it but doesn't set it. And we indeed use it in ScummVM if defined.

I am wondering if there is a reason to have two traditional chinese translation. But couldn't we have all three "zh", "zh_Hans", and "zh_Hant" in the themes?

I'm guessing that "zh_Hant" was intended to be a rename of the older "zh" to reduce ambiguity between the Traditional and Simplified translations when the latter was added. Since "zh_Hant" is empty it should still be relatively simple to remove it and rename the "zh" translation, I'm just not sure how to do that without disrupting Weblate.

I'm guessing that "zh_Hant" was intended to be a rename of the older "zh" to reduce ambiguity between the Traditional and Simplified translations when the latter was added.

Since zh_Hant and zh_Hans were added on the same day that is probably a good guess.

Since "zh_Hant" is empty it should still be relatively simple to remove it and rename the "zh" translation, I'm just not sure how to do that without disrupting Weblate.

I think we will need to do that manually, but lock Weblate during the process for safety. I will do that after your changes are merged.