A cunning ploy: Un stratagème astucieux
A fug of grief: Une gueule de chagrin
A white lie: Un pieux mensonge
After a good deal of practice
And I hardly need add
Anew: À nouveau
As you see fit: Comme bon vous semble
At point blank: À bout portant
Attagirl/Attaboy: Bravo
Behold!
Bummer: Dommage
But of course
Calm down
Can I speak plainer?
Capital offense
Cheerfully: Gaiement
Don't get ahead of yourself: Ne t'emballe pas, Ne mets pas la charrue avant les bœufs
For all intents and purposes
Getting one's hands dirty: Mettre ses mains dans le cambouis
I am all astonishment
I am quite determined
I beg you would excuse me
I don’t want no <something>
I have an ace up my sleeve: J'ai un as dans ma manche
I reckon it will come back to me
I shall trespass on your time no longer
I take my leave
I'm fully aware
I'm much exceedingly obliged
If you can help it: Si tu peux
In broad dailight : En plein jour
In shambles : En pagaille
In your stead: À ta/votre place
It cannot be helped
It's a piece of cake: Facile
It's raining cats and dogs: Un temps de chien
Keenly: Vivement
Kill two birds with one stone: D'une pierre deux coups
Last I checked
Let the cat out of the bag: Vendre la mèche
Make haste!
Mind your own business
Much obliged: Infiniment reconnaissant
My own better judgment
Neither of us
No please, don't trouble yourself
Nohow: Aucunement
None better
On a whim: Sur un coup de tête
Please convey my regards to
Save your breath
Seldom: Jamais
Somewhat: Quelque peu
Still waters: Eaux calmes
Sweetheart, sweetie
The blue book: Le bottin mondain
The charges levelled against someone: Les charges portées contre quelqu'un
The task will fall on you
Thither: Là
To arise chiefly
To ask after someone: Demander des nouvelles de quelqu'un.e
To be ill qualified
To be in the know for
To be off-limit
To be on par with
To be out of one's wits
To be shacked up: Cohabiter
To be torn over something
To be up to speed with
To be witty: Être spirituel
To behove: Être bon
To break stride: Ralentir un élan
To cut to the chase
To feel blue
To flog a dead horse: S'acharner, Perdre son temps
To get a word in edgewise: Arriver à placer un mot
To give somebody the heave-ho:  To take someone's job away from them, usually because that person has done something wrong
To go astray: S'égarer
To go out of one's wits: Perdre la raison
To have a will of iron
To intrude upon your privacy
To keep down the fluff
To let off the hook: Laisser partir
To make something easy on someone
To sow the seeds of discord: Semer la discorde
To stand idly by
To take a rain check: Remettre une rencontre à plus tard
To take delight in something
To tear asunder: Déchirer en morceaux
To think ill of you
To wriggle out of something: To avoid doing something that you do not want to do
Unwillingly: Contre son gré
Utterly: Tout à fait
What about him?
What's on your plate?
Whilst: Tandis que
With all due respect
Would you be so kind as to
You did good
You got a mouth on you boy