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The English names for the days of the week are all based on the Norse Pantheon equivalents of the Roman Gods for which the days were originally named in Latin. The Italian days of the week, lunedi, martedi, mercoledi, giovedi, venerdi, sabato, and domenia are named for the Moon (la luna), Mars, Mercury, Jupiter, Venus, Saturn, and the Sun (which became the Lord's Day, thereby Dies Domenica in Latin). The Germanic languages merely took the roles the Roman gods played and substituted in thier own gods: Mani for Monday (personification of the moon), Tyr for Tuesday (god of war), Woden (Odinn) for Wednesday (considered a psychopomp like Mercury was), Thor for Thursday (god of thunder), Frigg for Friday (goddess of love), and Sunna for Sunday (personification of the Sun).
Notably absent is Saturday, which retains its association with Saturn. Interestingly, the Italian sabato comes from Sabbata Dies or the Day of the Sabbath, showing that Italy, the origin of the Roman Pantheon was Christianized before the solidification of the names for the days of the week in its language while England, conquered by Claudius in 43 A.D. solidified Sæturnesdæg into the Anglo-Saxon language before Christianity was introduced in the Third Century. This is perhaps a clue as to the relative ages of the languages: Italian as a language did not evolve until the 900s by which time the country was firmly established as Christian while the Anglo-Saxon language descended from the Germanic (Frisian in particular) languages, which were notably pagan. Following this idiosyncrasy is Spanish, French, Romanian, and Albanian versions of Saturday being named after the Sabbath. Germanic based languages such as Dutch, German, Norwegian, Danish, Swedish, Finnish, and Estonian, all maintain the root linking thier versions of Saturday to the Roman god Saturn.
In oriental cultures, the practice of naming the days of the week after the sun, moon, and five visible planets (known as the Seven Luminaries) persists. In Chinese, Japanese, Korean, and Tibetan, the days are named in the same planetary tradition as western languages only the planets are namesd after the five traditional elements: Fire (Mars), Water (Mercury), Wood (Jupiter), Gold (Venus), and Earth (Saturn).