As a French, English is my default language for most queries on the web, but it wouldn't cross my mind to look up for a recipe in English. I also find that we have a lot of good science/maths youtube channels.

If searching for recipes in English, you need to add "UK" or maybe "Australia" to avoid the American recipes. (Avoiding US measurements and processed ingredients.)

But even then, there's still a lot of spammy or dumbed-down content. I look for sites I recognise.

What I had in mind is that I go to a local market every Sunday to buy some nice fresh food. But e.g. for the fish/meat I still only understand 1/3 or 1/2 of the names/terms. Nevertheless, I have read some lengthy tax code sections more than once in details... I do not cook like a French, and - oh - they cook really nice! :)

Try German, too. I'm always amazed at the level of German writing, even by regular joes on forums and Discord, compared to for instance Dutch writing.

I might. I hardly know anything about the German language though right now. Do you have a rough sense of how much I'd need to study to be able to supplement with automatic tools and do something useful with German sources (50hrs, 500, ...)?

Probably closer to 50 than 500, assuming you've done something similar before and you have "native" proficiency with another germanic language. Honestly, just read the Dover First German Reader, watch a few TV shows end to end with captions a couple times, turning them off and on and rewinding whenever. Read some german-language forums, and watch some German language talks. That won't get you anywhere near conversational proficiency nor develop any speaking skills, but more than enough to get great value out of written text and a lot of talks, especially with some tools to help.