Dies Iovis, Jupiter's day, named for Jove, another name for Jupiter, became Thor's day among the Germanic peoples, preserved in English as Thursday. The equivalence drawn between Thor and Jupiter rested on their shared role as the chief sky god of their respective pantheons and, more specifically, on both wielding the sky's characteristic weapon, Jupiter's thunderbolt and Thor's hammer Mjolnir, a resemblance concrete enough that interpretatio germanica matched the two gods more readily than it matched some of the week's other pairings.
The Romance languages again kept the Latin planet directly: giovedi in Italian and jeudi in French both preserve Jove's name without Germanic substitution, continuing the same pattern already seen in Tuesday and Wednesday, where languages descended straight from Latin carried the planetary names forward unchanged while the Germanic branch translated them into locally meaningful equivalents.
Sources Norse Mythology: A Guide to the Gods, Heroes, Rituals, and BeliefsJohn Lindow with Deutsche MythologieJacob Grimm