What are the most important search engines for my SEO in France?
Google!
With a market share of more than 90%, Google is the search engine that can't be ignored. For the overwhelming majority of websites, it will be the only search engine to worry about.
Of course, the traffic from all the other engines will always be good to take. But the volume will be insignificant and they won't deserve special attention, unless you have a very significant audience, a very large semantic universe or enough resources to allow it.
It is therefore useless to audit your visibility on other search engines or even to pay to register.
Anyways, please know that the SEO optimizations realized for Google will also work for the other search engines.
Most of the time, you will even be higher ranked on Bing and Yahoo than on Google.
