Super simple et efficace: tu sélectionnes un texte, bouton droit, menu "To DeepL" ouvre un nouvel onglet avec ce texte traduit.
Thanks to @rewkha :-)

Works really easily and nicely for me! The selected text opens up in DeepL in a new tab. Have been using this for a few years now and I don't think I have ever faced any problem with it.

Great open source addon. No permissions requiered, and a better translation than with Google Translate.

Make the work with great Deepl.com-translator easy, also for paying customers as me. Big thank you the the developer.

Great GoogleTranslate alternative.
Extension needs no permissions.
I can define translation target language in about:addons preferences.
Can be good if addon asks for setting destination language after installation or detect it automatically from browser settings. Maybe that would require more permissions though.

Better quality translation than Google's...much better. Little annoying to have to right click and then 'send' it to the translator. Should use the same trick as the others, i.e. a pop up logo after selecting text.

It does what it does. Within its limited language range, it performs much better than Google Translate.