I first noticed this while learning the planets in Japanese. I looked at the elements and compared them to days of the week, and realized they were like Italian.
Monday: lunedi -> luna -> moon
Tuesday: martedi -> marte -> Mars
Wednesday: mercoledi -> mercurio -> Mercury
Thursday: giovedi -> giove -> Jupiter
Friday: venerdi -> venere -> Venus
Monday: getsuyoubi -> getsu -> moon
Tuesday: kayoubi -> ka -> kasei -> Mars
Wednesday: suikoubi -> sui -> suisei -> Mercury
Thursday: mokuyoubi -> moku -> mokusei -> Jupiter
Friday: kinyoubi -> kin -> kinsei -> Venus
So I found this article.
"Before they adopted the Western-style week, the Chinese originally used a ten-day cycle known as a 旬 xún in ordering their daily lives and activities. Although the Christian week was not unknown (it was known, for instance, from contact with the Jesuits in the 16th-18th centuries), the seven-day week as we know it first became widely familiar in the 19th century with the coming of traders and missionaries from Western powers. It was finally officially adopted by the Chinese government in 1912, after the fall of the last Imperial dynasty.
Although the Western-style week is a modern phenomenon in China, the names of the Western days of the week were known from antiquity. The nomenclature of the seven planets -- naming of the days after the Sun, the Moon, Mars, Mercury, Jupiter, Venus, and Saturn -- had come overland from the West in the first millennium AD, resulting in a system of names translated into Chinese."
On the origin of this system and Japanese adoption of the system here.
"Although not in widespread use except for astrological purposes, this system of names was nevertheless maintained by the Japanese right through to the modern era. At one stage the days got out of kilter in eastern Japan and had to be rectified by a calendar reform in 1685. When they came under pressure to harmonise their working calendar with the West in the latter half of the 19th century, the Japanese turned to this old system to name the days of the week, officially adopting them in 1876. After this the names gradually came into general use in Japan"