Salut! French etiquette question: how does one sign off a friendly, informal letter?
Depends! Is that letter to a friend? Do people actually write letters to friends still...? I dunno. In any case, you may sign off with the very friendly bises, ‘kisses’ (as in, a smack on the cheek), or the childish, and therefore more affectionate, bisous (‘kissy-kissy’?). Je t’embrasse is also a solution, slightly more formal, more ‘letter-like’, for the appropriate occasion.
Now, if the letter you’re signing off is addressed to someone you don’t know that much but aim to be vaguely cheerful at, Cordialement generally is the go-to send-off these days. People use it a lot in emails, when the more pompous, rigid courtesy phrases often seem out of place. Recommended at the bottom of electronic letters:
Salutations/Sincères salutations/Avec mes salutations (Best regards)
Bien à vous (Yours truly)
En vous souhaitant cordialement une excellente journée
Avec mes remerciements (with my thanks)
If you’re so friendly that you’re at tutoiement level—first name basis, the whole shebang—you may write Bien cordialement (not so elegant but many people don’t know this), Bien à toi (a bit formal these days... my frequentations aren’t too posh, I guess), or circle back to the all-purpose Cordialement. You’ll always end up back at the Cordialement. Learn to hate people who manage to abbreviate it, hideously, into Cdlt, suggesting they’re too overworked to muster basic politeness. Hisss. @a-room-of-my-own!