Pick up a topic in which you are really good, in which you can analyse data pretty well and advice other people. Something you are good in.
Your blog would be useful for just those who knows about French language. But how would they cope who don't know French language?
Information is dynamic with virtual geographic area . You make it only for FRENCH language ,means that only for French,this is not dynamic ,this is static. Ok your idea is good ,many FRENCH will be satisfied . To earn popularity please make it informational and resourceful,give preference on local culture or local hot topics,update information regularly.
French is a virgin market that is really profitable. It's a great idea OP. If you know what you're doing then you're going to be earning serious money if you pursue it.
^ No problem. Do you already have an idea on what topic you would focus on? Make it very interesting and something French people would really be interested in. I'm not sure how Adsense works on foreign languages though. But I'm sure you already have an idea on how to monetize the blog?
Before starting, ask yourself what problem you're going to solve for your niche audience? Get your seo basics right and most importantly persevere at value creation. Best of luck!
Yeah, the most important thing is to measure niche for your blog. What will you write and provide the info in your blog? What? If you have decided then no one can stop you. You'll have to care of you users, solve your users problem in your blog. Which is the sign of a perfect blog.
You should pick a topic first and build your audience. Just be consistent and real. It is good if you can add Language Translation to your Blog as it will help foreign visitors to love your website even if they don't understand French.
Do some research using Google and specially for the french stuffs and then pick a topic and category and start a site on it.
if you pick a good topic where you can write many interesting and useful stuff, your blog will be popular soon enough