Here's a mnemonic means of learning or recalling the days of the week in other languages.
Think of the Sun, the Moon and the 5 bright Roman planets.
Only five planets shine visibly like stars (and yet move between them) in the night sky - Mercury, Venus, Mars, Jupiter and Saturn. Together with the Sun and Moon, these "moving stars" were thought in Roman times to rule one day each, and so were given the Latin names of Roman gods and goddesses. Hence the modern-day week has 7 days.
The English took their day-names from the Anglo-Saxons however, who substituted their own equivalent Norse gods/goddesses for the Roman ones, while the French and Spanish have adapted the Latin names over time. The whole makes an interesting table:
A separate page has mnemonics concerning the number of days in each month.
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