The EU plans to do so and as such every member must follow it.

And once encryption is criminalized, it can be trivially detected - or at least assumed to be encrypted if your message is sufficiently random.

We can keep them indefinitely then, right? If they’re not doing anything there is no need to ever revoke them.

Not necessarily, there’s regional languages such as Catalan. The phrase is kinda iffy considering what Spanish nationalists think of those languages.