Hmm... from scratch? Some basics? How long is a piece of string! It depends on a variety of factors - motivation is extremely important, along with persistence... especially for those who are a while past their prime learning years! A knack for languages, a musical ear. A good memory. All play a role.

A good learning method is vital too, and online systems are not ideal imo, being rather impersonal and lacking in quality in some cases.

To get some ability in the language before arrival, taking a French class is best imho, or if not some sort of cd learning pack.

Once in France, the more contact with French people the better of course.

It can seem an impossible task when you set out, but there's a kind of comprehension threshold where you begin to understand about two or three words in ten... and miraculously you start to have a clue what people are on about! A vocab of 'just' a few hundred words does the trick. You might be surprised just how limited the average use of vocab actually is, in the course of most conversations, over a normal day.

I haven't taught for a while, but I'm a professional linguist - a qualified translator and interpreter... so I speak from a little experience, but not so much from the learning a European language perspective as it's a while (a few decades) since I had to do this from scratch. Still I spend half the year in Thailand at the moment, so I empathise with those worried about coping with the language change. But unlike me, at least new arrivals in France aren't having to cope with a lingo written in hieroglyphics!!

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Pete - Long-term property rental in Provence - My Flickr photostream