Romance Language Hobbit Names

Tolkien establishes that Westron is translated as English, and other Mannish tongues are 'translated' as other Germanic tongues by analogy. (eg. Rohanese is Old English, Dalish is Old Norse)

However, some Hobbit names, especially among the Tooks, are based in Romance languages: Gerontius (the Old Took) (Latin, Greek influence), Belladonna, Mirabella, Donnamira (Italian), Fortinbras (French).

Obviously, in the 'untranslated' Middle Earth, such names would almost certainly be different, however we have little precedent for what languages are being 'translated' into Romance languages. My gut instinct is to say one of the Elvish tongues, especially given the Tooks' relative world-wisdom, but I could be wrong.

The Tooks' adventurous nature is a fair point. If it is one of the Elvish languages, it must be Sindarin. By the 3rd age, Quenya is used only to preserve old lore or by a handful of lingering High Elves.

However, Sindarin outside of the Shire is not translated into anything except English, and that happens when it has in-story Westron translation - as far as I remember. Of course, it may be different if the Hobbits use it for themselves...

For me, it simply came across like the Hobbits are speaking a more modern (and probably more careless) version of Westron, then e.g. Gondorians. In LotR, in Ithilien Frodo and Sam percieve the Rangers' Sindarin as archaic compared to their own. As you have mentioned, Westron is represented by English, and English even by the Middle-Ages has been much influenced by Latin and French (beside other languages of various language families), and this influence is an unaviodable part of modern English. So having names from various origins make the Hobbits' dialect more modern and everyday style.

This is, again, just my interpretation. I don't know whether there is any information from Tolkien about the origin of these names. But it is a good question.