Language in the Regency

In the Rush memoires I read that the English upper class larded their speech with French, despite being at war with the French. This is obviously true of Italian, also, judging from this letter from Theresa Fielding to her son. They are both part of the influential Fox Strangeways family. You can read the notes here.
http://www.foxtalbot.arts.gla.ac.uk/corresp2/00677.asp

Sackville Street<1>

20th Decr (1815)

My Dearest Henry

I am so pleased that you liked your parcel, you have no idea di quel gran piacer ch’ío gusto nel farvi piacere.<2>

I will send you Zetti’s Grammar<3> but will wait till I hear again from you, in case you should recollect any thing more you wish to have sent with it.

I have sent to Rodwell for the last Edition of Zetti’s Grammar, but it is not yet come. & I will look over my Italian Books to see if I have any that will suit you. You are too young yet to read their first rate Poets, you would not yet feel their beauties, & they are difficult. I will must send you some easy books to begin with, & in prose till you are more au fait<4> of the language

Adiò conservatevi & scrivite Subito<5>

Let me know if the Morning Chronicle<6> ever miss because I send it every day

Have you a good Italian Dictionary to consult?

Would you like to have the Examiner?<7>

William H Fox Talbot Esqr
Rnd Mr Barnes’s
Castleford
Ferrybridge

A letter from his sister is entirely in French. An exercise to some extent, but indicative.
Ce 11 Fevrier 1817.

Mon cher Henri,

J’espère que vous êtes bien content d’avoir aujourd’hui dixsept ans, je vous le souhaite de tout mon cœur & je voudrais bien avoir le plaisir de vous le dire de vivevoix.

Maman<1> nous a fait présent à chacune d’une très belle poupée, et nous allons célébrer votre jour de naissance en meublant les petits appartemens des poupées, c'est à dire notre Baby House. Il faisait clair un soir, mais Maman ne pouvait pas nous permettre de regarder les étoiles à cause du Froid.

Mon cher Frère
Croyez moi
Votre affectionnée Sœur


Caroline Augustine.

London Feb eleven 1817 Auckland<2> –
Hy Fox Talbot Esqr
Revd Mr Bonney<3>
Normanton
Stamford

Translation:

11 February 1817

My dear Henri,

I hope that you are happy to turn seventeen today, I wish you this with all my heart and I would so like to have the pleasure of saying this to you in person.

Mama gave each of us the gift of a very beautiful doll, and we are going to celebrate your birthday by furnishing the little appartments for the dolls, that is to say our Baby House. It was clear one evening, but Mama could not allow us to look at the stars because of the Cold.

My dear Brother
Believe me
Your affectionate Sister
Caroline Augustine.

All the letters are interesting.
http://www.foxtalbot.arts.gla.ac.uk/