A spell checker, grammar checker, and tutor change a relatively small fraction of the writing, preserve the writer's style/voice, and rarely introduce errors that are hard to detect like hallucinations.

A translation app changes nearly 100% of the content, often changes the writer's style/voice, and can introduce hard to detect errors. But there's a far closer correspondence to what was written by the original writer. The basic ideas are still from the writer. A translation app is not expanding a short idea into something longer, and including some things the original writer never thought in the process.

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Pre-LLMs, I did in fact disclose when I was using a translation app in some translations of scientific articles I produced. It would be weird to disclose the use of spell checking, grammar checking, or who previously taught me writing as these things are ubiquitous. I will also acknowledge people who were influential in my thinking. If a LLM is doing a lot of the thinking for me then I do think disclosing LLM use is appropriate.

I find it's incredibly helpful to know when someone's using an automated translator, as they usually get details wrong while still reading like a native speaker. Not using a translator at all, or disclosing that one was used means I can make a better educated guess as to what they mean. It also changes how I reply.

If there were groups that voiced a desire to be informed of that, then it would indeed be courteous to do so.

It used to be the polite thing to disclose that you used a translation app. In fact, traditionally, you disclose when you translate anything so people know the context in which to interpret your text.

In the same way, I wanna know if a book is written by some famous people just ghost written.

Of course, the point is moot. Somebody using AI to write a blog post is unlikely to be self conscious enought to thing it's necessary to disclose it in the first place.