In general, it’s easier to start different topics for different questions. Then both can have a title that describes what it’s about, and it’s more likely someone knowing the answer will read the topic and reply.
The Discourse interface is translated to French, currently about 94%. You rarely see 100% because new features, and with them new texts, are added almost daily. Everyone can help to translate Discourse. There is also a translation agency working on adding missing translations and ensuring consistent translations. These translations are part of Discourse, you don’t need a separate file, and new translations are also included in the Discourse updates.
Admins can also change any text in their forum, so if a specific text is quite important for your community and has not yet been translated, you can immediately change it by customizing the text.