Answer

By Country Walking magazine

There are a number of English-language guides to the Pyrenees, but few which concentrate solely on the French side. General interest volumes like the Rough Guide to the Pyrenees will give an overall feel of the region, while companies like Trailblazer produce a hiking specific one Trekking in the Pyrenees. 

It's also worth looking at particular routes; the Grand Randonee 10 runs coast to coast through the French Pyrenees and Cicerone produce an excellent guidebook - The GR10 Trail.

Cicerone also produce a superb book on both hiking and climbing, Walks and Climbs in the Pyrenees. Again, it's not specific to the French side, but offers a wide variety of outings. And check out their website - the entry for this book has a Further Reading section which includes a long list of useful books covering general and landscape information, plus walking, trekking and climbing guides.