I am sorry if I look pessimist. I didn't mean it.
Every piece of advice, is a piece of golden advice. There is no definite answer.
Here is my other 2 cents: Virgin Markets can be dangerous. It takes too much time to develop or a lot of investment, or both. Make tests on different languages and check what is more efficient for your purpose.
First of all, I thank you all for these answers. My wife invested four months of research on the articles so I do not want to let her down.
The main idea that appeared several times was to use another language, so we will follow your advice. We will first translate it in English (we will see for French and maybe German later) since it has the most important audience. I will the be able to test the adsense revenue.
I will let you know what the results will be. Thank you again for your help and time!