Christ was a Jew and HE observed the 7th day of the week not the 1st day of the week. His own mother observed the 7th day after his death. The Jews have continued to observe the same day of the week that Christ observed until today. Paul 's observance on the Sabbath was documented more than 70 times in the NT.
Here are what some various languages call Saturday.
Arabic: Sabet
Armenian: Shabat
Bosnian: Subota
Bulgarian: Sabota
Corsican: Sàbatu
Croatian: Subota
Czech: Sobota
Georgian: Sabati
Greek: Savvato
Hebrew: Shabbat
Hungarian: Szombat
Indonesian: Sabtu
Italian: Sabato
Latin: Sabbatum
Maltese: is-Sibt
Polish: Sobota
Portuguese: Sábado
Romanian: Sambata
Russian: Subbota
Serbian: Subota
Slovak: Sobota
Slovene: Sobota
Somali: Sabti
Spanish: Sabado
Sudanese: Saptu
Ukranian: Subota
Catholics observe the day of the Sun not the Sabbath. In fact they claim changing the day is a mark of their authority over God's law.
Reverend Steven Keenan’s Doctrinal Catechism we read this: “Question: Have you any other way of proving that the Church has power to institute festivals of precept? Answer: Had she not such power, she could not have done that in which all modern religionists agree with her; she could not have substituted the observance of Sunday, the first day of the week, for the observance of Saturday, the seventh day; a change for which there is no Scriptural authority.”
Saturday is the Sabbath of the 4th Commandment not Sunday.