2.1 is a lower bound. The bulk is directory language. You could apply filters to httrack. And apply some html compression to the output. Or convert it to pdf, and then compress it. Have a look here and here.

PS: I confirm that this will load quickly:

httrack https://reference.wolfram.com/workbench -https://reference.wolfram.com/language/*

It's bloated.

httrack https://reference.wolfram.com/workbench Mirror launched on Tue, 29 Mar 2022 00:46:33 by HTTrack Website Copier/3.49-2 [XR&CO'2014]

Hello Sander, Yes, I think it shouldn't be too hard too. I've thought about doing just that. I imagine that I'll just keep thinking about it.

Like E-hern Lee, I've wished to have an offline documentation.

I like to read on my tablet device. For the WL, I find the html documentation too slow.

Another issue is that I tend to "modify and evaluate" too quickly when using the live documentation and should probably be reading more thoughtfully. I believe that I learn more about the language when I read the on-line documentation,. The live documentation is more useful, yes, but my interaction mode is different.

I'd pay up to $100 for a tablet-readable no-kernel version of the documentation. It would need to maintain the link structure and could have down-sampled images. However, I imagine that the full documentation would be too large to fit on a tablet: the documentation appears to be 3.7GB on my Mac and would probably get larger if graphics objects were converted to images.

I would also pay for an abridged version of the documentation with just the function listing, their arguments, Detail section, and with (all) Options.

Just my 2 cents---or $100.

Mathematica includes the documentation, apart from that (to my knowledge) there is no downloadable documentation.