If your main deck contains Chinese cards, must all cards be in the same language, and does this rule apply separately to each deck (main deck, runes, battlefields, legend)?

Ruling: The language restriction applies separately to each deck. If your main deck contains any Chinese cards, all main deck cards must be in the same language, but runes, battlefields, and legend decks can be in different languages.

Nuances:

• The rule exists because Chinese cards are printed differently and have a different thickness, so players should not be able to distinguish between cards in the same deck
• You could have all main deck cards in Chinese and the rest in English, or just the overnumbered Chinese legend with the rest in English