"The telescreen received and transmitted simultaneously. Any sound that Winston made, above the level of a very low whisper, would be picked up by it; moreover, so long as he remained within the field of vision which the metal plaque commanded, he could be seen as well as heard. There was of course no way of knowing whether you were being watched at any given moment."

There's likely far more identifiable information in the actual text than a user ID provides.

Cloud assumes a constant, reliable internet connection, which is not the reality in most of the world. (Nor is it always desirable.)

If the data never leaves your device, then a third-party service never gets the opportunity to leak or misuse it. This is far more private.

How many stories have you heard about breaches due to accidentally mis-configured logging in web services? Also in the news lately was Twitter misusing 2fa phone numbers for advertising purposes.

What if what I'm trying to translate is sensitive information in itself?

In the current status quo you either make use of an api by indentifying yourself with a key or a browser session that is fingerprintable in a gazillion ways. There is no such thing as "not sending user ID" or if there is, it has a totally negligible reach.

If local translation can help me use a website without a query to some cloud server... who needs the cloud? No backend that will experience downtime, and someday be decommissioned. No money sink of cloud processing pressuring the product to advertise or monetise in unscrupulous ways.

I'm sure cloud processing is better in many ways. But if this is "good enough" I'd rather just do it all locally.