trois semaines
It depends what you want to say. For example, if you want to say there's three weeks left before Christmas, say "Il reste trois semaines"
Huit semaines. Please not that all numbers must be written out in French.
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les semaines
Deux semaines
The way you say "three chicks" in french is "trois poussins"
'Home for three' in French is 'Maison pour trois'
Not exactly see you in a few weeks but, à bientôt means see you soon. Vous voir en quelques semaines, I believe means see you in a few weeks. You can say Salut or au revoir to say goodbye.
trois
We pronounce three as trois.
You would say "J'ai trois chats" in French to express that you have three cats.
You would say "J'ai trois filles" in French to indicate that you have three daughters.