This requirement arises in the following cases:
You have a website/app in two or more languages
This situation is the most common and occurs when two (or more) completely different sets of users are targeted. It’s best that the documentation be available in all the languages in which your site/app has been translated. The purpose of the policy is in fact for the owner to fulfil his obligation to inform the user with regards to how his or her data is to be collected and processed.
When the policy addresses users in a certain language only, while the site addresses them in their own language, then these users will not be properly informed about the data processing (you can’t assume that everyone reads and understands English, for instance).
Your app is in one language, but you’re based somewhere with another official language