It's a common problem I had in South America - I really wanted to improve my Spanish while travelling as it gives you a much better insight into your travels, and can talk to locals more.
But so often they'd just switch to English because they welcomed a chance to learn English themselves.
You can either do the obvious (ask them to speak French so you can learn) or what I did occasionally - we'd hold dual-language conversations - I'd try speaking in Spanish and they'd speak in English, as it gives you speaking practice - the hardest of the language skills, in my opinion.
Alternatively, you can switch -
you speak English, they speak Spanish, and you both get to practice listening skills in the language.
Remember that travelling is a shared experience, they welcome visitors to their country (well most of them do), and if you can both benefit from a conversation, everyone wins!
travel.stackexchange.com/users/101/Mark Mayo
Just ask them.
If they switch to english, say: "S'il vous plaît, en français, j'essaie d'apprendre."
travel.stackexchange.com/users/241/mouviciel
One thing you could try: Learn a few phrases in an obscure third language.
I speak Romanian, for instance.
So if I'm in France and trying to learn French, and they reply in English, I just give them a polite but blank look and say, Îmi pare rău, nu înțeleg.
Of course, the risk is that they'll decide that you're not worth the trouble.
So it just depends on how determined you wish to be.
travel.stackexchange.com/users/2618/Kyralessa
Don't stress about it too much.
Sometimes I have to remind myself that learning a language is a means to an end, rather an end in itself.
You didn't go to France in order to learn French, you learnt French in order to go to France.
Beware of the sunk cost fallacy - don't let the time and effort spent learning French unduly influence whether or not you use French.
I tried to speak in Japanese when possible when visiting Japan ("sumimasen, eigo o hanashimasu ka?
" was usually a sign I was going to ask something complex!), but I made an exception for the sweet obasan who ran the ski hire shop in Zao onsen.
She asked me to speak in English, and I did so.
Are you going back to Paris, or to France in general?
You may want to check whether going to the more remote parts of France will mean people less likely to speak English.
Then again, it could mean that those who want to speak English will be more insistent on speaking English than those in the middle of Paris!
You may also want to check whether France's colonies or former colonies tend to speak English less than France.
That's an advantage you have over Japanese speakers - the only place outside Japan with Japanese as an official language is the island of Anguar, population 188 !
travel.stackexchange.com/users/324/Andrew Grimm
I know there is already an accepted answer, but I thought I'd throw in my two cents anyways.
My advice - just keep speaking in French.
Be more insistent than they are.
If they continue to attempt to speak in English just say something along the lines of: "Would you mind if I continue practising my French?"
There's a chance, of course, that they will not let you speak in French at all, and continue in English no matter what.
If that's the case, and you don't wish to continue any battle of wills, just concede, and speak in English.
You can of course always ask them later (or better yet, before!)
if you can conduct conversation in French, "even if I make some mistakes".
BTW - here's a pretty cool article about the topic.
travel.stackexchange.com/users/36151/galois
Wow this is very interesting, what happens to me and everyone I know in Paris is the exact opposite.
I speak English and they reply in French always, in fact i stopped going to paris for that reason.
No matter how many times I say I don’t speak French they just insist to, and what kills me is that they clearly understand me
so they know English
but I don’t hear other than French.
I’ve also noticed that this phenomenon decreases as you go further away from Paris, people seem to be friendlier elsewhere in France.
travel.stackexchange.com/users/1287/msk
From my experience it may be because your French is not good enough and it causes pain to their ears and some actual comprehension difficulty.
On several occasions I have found myself in France with Anglophone companions who had no problem speaking with locals, whereas the locals rather preferred English when speaking with me.
I do not take this as an insult-
it's their beautiful language I'm butchering.
I would suggest trying to get the pronunciation
exactly right- vocabulary and approximate pronunciation is not good enough.
travel.stackexchange.com/users/12046/Spehro Pefhany
I went to Paris 2 years ago. When I was there, I was learning the language by talking and listening to the local people. But, while I was trying to speak French with them, they would speak English to me. I am going back this november. What can I do to get them to speak French?
How can I get people to speak the local language to me?
travel.stackexchange.com
<france><paris><local-customs><culture><french-language>
travel.stackexchange.com/questions/2832
travel.stackexchange.com/users/1029/Daniel says Reinstate Monica
It could be that they are struggling to understand, but don't stress about it too much and try to continue speaking in French, or say: "S'il vous plaît, en français, j'essaie d'apprendre." You could also try going to areas where less English is spoken, or have dual-language conversations where both of you can practice.  Sometimes it is difficult to practice a language because native speakers tend to answer in English. It is considered a good idea to ask them to speak in their language. It is also possible to continue speaking their language even if they answer in English. However, be aware that they may find you difficult to undertsand. It is best not to stress about this too much.
If you want to practice your French, just ask people to speak French. S0: Don't stress about it too much. In places outside Paris people may speak less English and therefore they will speak French with you.  If your French is not very good, people may find it difficult to undertsand you. Keep speaking French.