About 905-906 the Latin Rite took the place of the Slav Rite and Bohemia was assigned ecclesiastically to the Bishop of Regensburg and the metropolis of Salzburg. However, it is worthy of note that about the middle of the tenth century, at the time of Saint Wenceslaus, there was still a strong intermingling of the elements of both rites, and an advanced coexistence of both languages in the liturgy: Slavonic and Latin. Moreover, the Christianization of the people was not possible without using the native language. And only upon such a foundation could the development of the Christian terminology in Bohemia take place, and from here, subsequently, the development and consolidation of ecclesiastical terminology in Poland (#23).
As I said, much like St. Nicholas, JPII uses Wenceslaus as a unitive figure or landmark in the evangelization of the Slavic peoples. He represents an infiltration of the Gospel into the language, hierarchy, and customs of the Slavs, to such an extent that royalty even identifies with the language and message of Cyril and Methodius. Only a century after the Saints evangelized the region, Wenceslaus and others fully incorporated the life of Christ in the day to day, to the point of shedding their blood for Him.
In regard to Christmas, St. Wenceslaus is famous for the following line from "Good King Wenceslaus":
Good King Wenceslaus looked out on the feast of Stephen! (Dec 26th)