[x] Changing only the quantity of the SKU in a foreign language will reset the language to English, even if you tick the Language to apply to something other than English. Example, update the quantity of a 10 qty SKU of JP Island. The language of this SKU will change to English afterwards. (UPDATE: I strongly believe this is fixed by d47be6a783bebeab157eb2a13fde57a3b9b654d8)
[x] Collector number is lost on the freshly split SKU