I use Google Maps to plan my bike routes inside Paris. However, it is missing height graphs of the routes (which is essential for biking). I would like such a site that would be capable of this. I may be Paris-only and in may be in French.
When using OpenRouteService, once it has calculated your route, then in the Extras/Download area there's a link for Route Profile. Click that, wait while it processes, and you'll get the profile you're after. You get profiles that look a little like this:
If you want to try it out, and see a steep climb profile, try this link and then click the Route Profile when it has loaded. It's a long long climb up from the centre of Heidelberg to the lookout above it, but much more fun done the other way round ;-)
OpenRouteService will work anywhere there's good OSM coverage for, so you'll be fine in Paris, but you might hit the odd area in the countryside without all the off-road routes. It's available in a few language, including in French, so that part of your question is covered too!
You could use GPSVisualizer. You can easily plan your tour with Google Maps or whatever tool you like and then use GPSVisualizer to genera a height chart.
For example I used Google Maps to navigate from Sacre Coeur to the Eiffel Tower:
And here is the corresponding height profile:
Update: A couple of years after this question was first asked, Google Maps started including elevation data as part of their cycling directions. I don't think the coverage is universal, but it does include much of the US and Europe.
Garmin Connect http://connect.garmin.com/course/create
I can't screenshot, but here is a screenshot of it:
Then pop it into your garmin device for directions on your bike :)
You can use komoot, a well working bike and hiking planning tool. Also available as an app offering offsite maps but those have to be payed for (Paris is available for about 4€).
I only used it for Germany yet but it also knows about the paving!