There must be some links between French and English where in French, the formal version is "vous" which sounds like "you" and the informal is "toi" which maybe sounded like "thou" in the past. (The 'th' has no equivalent in French)
Yes. The tu and thou pronouns are related. So are me and moi, nos and ours. In Hindi me and you are mai and tu. In Russian they are menya and tubya. (Sorry for errors in transliteration.). English I and Fench je are related too. Old English ich and Latin ego make the link more obvious.
Pronouns tend to be some of the most fixed words in a language, up there with numbers and basic words like for "water" or "mother". They undergo sound change, and shifts like how English lost thou, but they are almost never replaced wholesale.
All those languages are in fact descended from a common language spoken several thousand years ago. About half of the world today speaks a language in the Indo-European language family.
That's because they're very closely related languages. English is a mix of Anglo-Saxon and Norman French, after the Norman invasion of England in the 11th century. Norman French is how the Norse diaspora in Normandy mixed their Germanic tongue with the local dialects of Latin. And the Romance and Germanic languages are both pretty closely related branches of Indo-European, which is also a pretty narrow language family to start with. For example, 'tu' from French comes from mixing Norse 'du' with Latin 'tuus'...both of which come from deeper roots. Proto Indo-European reconstructs this as 'tuH'.
There's no need to explain French tu by looking at Germanic languages. It descends pretty uneventfully from Latin tū. However, French and Latin tu are cousins of German du and English thou.
French and English coexisted as neighbor languages for more than a millenium, so there are a lot of both subtle and obvious similarities between the two.
The English T-V distinction seems to have originated after the Norman Conquest, where French became the language of the aristocracy; wouldn't be surprised if that was exactly the source.
