At the moment English is the only supported language in CookBook.
The app will not function fully in any language other than English, however we do have many users who have found that it can work quite well despite this. Unfortunately we cannot guarantee that all features will work if you are importing recipes that are not in English (such as the importer).
Translating the actual words within the app is a small part of the task, the main complication is the functionality running behind the app, for instance named measures converting, scaling etc. This all gets a lot more complicated with reading and detecting in different languages.
Translating CookBook into other languages is definitely something we would love to do in future but it's not on the roadmap just yet. We will reach out to all of our awesome users when we come to implement additional language support as many of you have already emailed offering to help us with this! ❤️