Hi mueschel,
Thank you for your reply.

>> first the language, then the direction

Got it. Thanks!

>> tag only the languages which are actually listed on the sign

You are right. The signs do list English destinations, but not Chinese Pinyin (i.e. ISO 7098 romanization) ones. I usually provide romanized names for the purpose of helping non-Chinese users getting its pronunciation; however, it does not make sense for navigation purpose, as users are expected to see it instead of read it.

>> It's not necessary to have both a destination tag on the way and a destination sign relation.

Will having both of them cause troubles? I did it for compatibility reason, as the support for destination tags and/or destination_sign relations may vary among data consumers. If their coexistence are to cause adverse effects, I will prefer destination_sign relations, which is more flexible and has the advantage of associating destination information with actual signs.