(well, thanks to synagogue my Hebrew is okay, just as long as I never try to talk about anything except God and His eternal glory.)
Every time I try to learn a language I buy books that promise "Revolutionary New Language Learning Technique!" and have quotes on the cover about "Instead of boring grammar and rote memorization, we make learning easy and natural!" And then when I open up the books...it's page after page of boring grammar and rote memorization.
I've been trying to think of what a language-learning course that actually wasn't boring grammar and rote memorization would be like, and whether such a thing would even be possible.
So imagine this - I'm going to use Japanese here because it's the only language I could even remotely try to use as an example without making a total fool of myself, and I'll thank you for not correcting the inevitable errors. The course is a novel. Could be any novel, but I imagine for cutesiness reasons you'd want to use a classic from the culture you're studying, like The Tale of Genji or Death Note.
The first chapter is just the first chapter of the novel in English. It would contain normal English sentences like "Ryuk taught Light the secrets of the Death Note."
The second chapter is still in English, but it's a weird English with a sentence structure a bit more reminiscent of the foreign language. It might change to something like "Ryuk the secrets of the Death Note to Light taught". (I'm keeping the sentence the same to make it obvious what's going on here, but of course in the real book it would be the second chapter, not just a repetition of the first).
The next chapter would do the same thing, but get a little more foreign, maybe "About Ryuk, secret of Death Note to Light taught"
And gradually it would get a little more so: "Ryuk-about, Death Note-of secret Light-to taught."
There would be enough of this that sentences with Japanese syntax would become as quickly and effortlessly readable as sentences with English syntax. And the hope is that the reader would keep going because they'd be enjoying the story, and after a little while adjusting the weird sentence structure would be a comparatively slight barrier to further progress.
Then some of the grammatical particles would switch to full on foreign. Now it's "Ryuk-wa, Death Note-no secret Light-e taught." Gradually we'd get through all of the horrible little verb bits where my language studies have previously crashed and burned: "Ryuk-wa, Death Note-no secret-o Light-e teach-mashita."
I might grudgingly allow little footnotes at the bottom like "This is the first time you've seen -mashita. It's just the standard past tense ending for verbs", but even that might be an unacceptable surrender to the grammar-memorization-industrial complex.
Finally, and very gradually, it would start replacing English words with Japanese words. Just simple ones at first, ones that were obvious from context, and of course there would be a glossary in the back of the book you could look them up in if you had trouble.
Finally, the last chapter would just be completely in Japanese: "Ryuk wa Desu Noto no himitsu o Light e oshiemashita." It would probably be very deliberately simplified Japanese, but still, if you can read a book chapter in Japanese that seems like a pretty good success condition for an Intro Japanese textbook.
(and of course Japanese is a bad example here because you'd have to learn the writing system separately. I'd have preferred the example in Spanish, but I'm not confident enough in my Spanish even to do a simple example sentence.)
I don't know if anyone has tried this before; it's really hard to think of the right Google keywords to look for it, and language learning searches tend to get bogged down in a bunch of advertisements for the latest courses. But I'm really curious whether this would work and regret that I don't know any foreign language well enough to try writing such a textbook and testing it. Anyone who wants to has my total permission and support.