French equivalent of 'I will let you know'
Hello, I have stumbled upon another phrase I have no clue how to say in French and I couldn't find a consistent phrasing online either. I am trying to book an air bnb and I want to tell the person "I will let you know what we are going to do soon" Does "je t'annoncerai ce qu'on va faire bientôt" make sense?
There is actually a very common idiom meaning "I will let you know" or more precisely "I will keep you informed/updated", it's:
Je vous tiens au courant.
In your case you could say for example:
Je vous tiens au courant de notre décision.
Je vous tiens au courant de ce que nous allons faire.
If you want to add the "soon" meaning in this, you may add "dès que possible" (it literally means: as soon as possible) or maybe "d'ici peu" or something like that.
Annoncer is a bit too formal in my opinion for this type of situation and the placement of "bientôt" gives the impression that you will soon give out information regarding what you will do rather than give out information regarding what you will soon do (if I correctly understood what you wanted to say). So, the better way to state your sentence is "Je te dirai ce qu'on va bientôt faire."
Otherwise if you don't know this person, it would be better to use the subject pronoun vous and perhaps keep the verb annoncer.
Je vous annoncerai ce que nous allons bientôt faire.