When I change from English Language to French, the language remains english and the calender is shown in english instead in french.

I have this problem too.

Maybe we are the only two user of this extension who do not use English Language ?

In my case, I have to chose the language from the extension window panel to make it work. The user interface however still shows English on the select even though I chose different language.

In the properties, language is always English. To see the selected language, I have to go to the Advanced window. It's really annoying and it takes time to go and check that the dates are set in the correct language. I live on the border between Switzerland, germany and France and I often have to change the parameters of dates.
It's still a very good product.
Gérard

Yup it still a good product, only some annoyance. There are also other bugs I don't bother mentioning since I don't really use it to that extend and the support is not so welcoming. And I hate it when the code writes calendar2 when it's really calendar 3. I have a feeling the dev didn't rewrite the code entirely but just update from previous version instead.