Rebonjour, j'ai donc un deuxième devoir pour le CNED, et si je pense avoir fait moins de fautes que le premier (merci encore de vos conseils), je sais néanmoins qu'il doit en subsister plusieurs...

Donc si cela ne vous dérange pas je vous invite à lire mon texte et me dire s'il y a des erreurs.

Dear Samuel,

As you said in your letter, today is my birthday!

I’m glad you don’t forget it and I want sincerely to thank you. Now I’m thirty, I know this is an important moment of my life…

Recently, I’ve found a new job. I admit it’s not what I expected… Since two weeks now, I’m waiter at McDonald’s. It’s really a difficult job, believe me. But I’ve not the choice, and before I will find a better job I’m forced to do that.
Just for the joke, if you come at the restaurant, I’m being very happy to serve you!

For your charity I find it’s a really good idea!

I would come participate with you, but with my working hours I don’t have free time. I’m sorry Samuel…

But my holidays begin in six weeks, so if you want we will meet at this period…

I miss your presence, I really want to see you.

I hope you like your job. And how are your children and your wife?

The last time you told me your daughter was sick… Is she well now?

You know I like so much tennis, so obviously I would come to go to Wimbledon with you! And if we could be at the final, that will be great…

But for the moment I’ve to go to at McDonald for working.
I hope you answer soon.

Bye,

Gerard.

PS : I’ve a new girlfriend!

Merci d'avance.

"I admit " correct, néanmoins j'te conseille de mettre "I have to admit", ou "I have to say".
"Since two weeks now, I’m waiter at McDonald’s" --> I've been a waiter for 2 weeks."
"really a difficult job" --> "It's a really diff.."
But I’ve not the choice, and before I will find a better job I’m forced to do that. " ... de la nooberie en barre ça. "But i DON'T HAVE the choice, and before I CAN FIND a better job, i'm stuck with this one" (pour le coup du stuck, c'est bieeen plus idiomatique).
"Just for the joke, if you come at the restaurant, I’m being very happy to serve you! " Vire "for the joke", et mets juste "Thus, i'll be happy to serve you if you come to the restaurant". (wtf, t'as un job de merde à macdo et tu l'invites en plus... WOOT)
"For your charity.." --> "concerning your charity, think it's..."
"I would come participate with you, " --> "I'd really like to come and participate, but...."
"your children and your wife? " --> juste "how are your Children and wife"
"Is she well now? " --> "Is she feeling better now?"
"I would come to go to Wimbledon with you" --> je sais pas ce que tu veux dire exactement, mais c'est soit "I would LIKE to come" ou "I WILL come".
"But for the moment I’ve to go to at McDonald for working." --> "But currently I have my miserable job to attend to."
"PS: I have a new girlfriend". c'est ultra moche de mettre "I've" tout seul au milieu d'une phrase si courte.

Un conseil général: T'as l'air de te démerder (si t'as pas fait ça avec google translate), mais des fois t'as des formulations cheloues. Essaie de pas trop tenter l'impossible quand t'as un doute. L'Anglais enseigné par l'école française est nul à chier de toute façon, tu seras bien moins pénalisé si tu fais des phrases cons et pas trop osées que si tu tentes des jolies phrases et que tu dis n'importe quoi (mais l'intention de le faire est très bonne).
Bonne chance

Merci beaucoup (avec du retard).

Non je l'ai fait seul enfin dico parfois pour quelques mois (genre serveur en anglais) mais sinon oui après effectivement y a eu quelques phrases bizarres j'essayais de faire copier/coller français/anglais dans ma tête mais oui faut que j'arrête de faire ça ça donne pas des trucs bien.

En tout cas merci à toi c'est vraiment sympa !