Acts 13:46-49; Ps 117(116):1. 2; Luke 10:1-9
and you are right, the Roman Church does not notice the popular St Vallentine in the liturgical calendar:
In 1969, the Roman Catholic Church removed St. Valentine from the General Roman Calendar, because so little is known about him. However, the church still recognizes him as a saint, listing him in the February 14 spot of Roman Martyrolgy.
The legends attributed to the mysterious saint are as inconsistent as the actual identification of the man.
The two brothers, Cyril and Methodius, were both educated in Constantinople and sent to Moravia to preach the faith. They translated the bible into Slavonic, and are credited with two alphabets - the Cyrillic, and more certainly the Glagolithic - although few will have heard of that one! They were however actually conceived by followers of the saints some generations later!
Nevertheless, the main blessing to come from the brothers is their taking of the faith to the slavic peoples, despite considerable political (in-church, sadly) opposition.