以下内容出自WIKI
Denka (殿下) is used for non-sovereign royalty, similar to "Highness". For example, Kako Naishinnō Denka (佳子内亲王殿下, "Her Imperial Highness, Princess Kako of Akishino"), and Suwēden Ōkoku, Vikutoria Ōtaishi Denka (スウェーデン王国ヴィクトリア王太子殿下, "Her Royal Highness, Crown Princess Victoria of the Kingdom of Sweden"). Denka can be used by itself, equivalent to "Your Highness."
至于Ritter是比Knight大一级的骑士阶,就叫「大骑士」吧(胡言乱语中