Hi Bhante, 
It never worked for me either, and I tried it every other year since the feature was first introduced. It has always been an experimental feature, I belief. Nobody seems to know why it works for some but not others. (If you do ever get it to work, please give me nudge.)
The legacy version has almost everything I need, though, and it works fine offline. (download here) Use it together with epubs of the translations, and you got almost all the content of the website offline, even though in a different format.
Let me add here also as an official bug report that installing the offline version makes the site significantly slower, in Firefox on Windows 10, even if the offline function doesn’t work.
See here. Snowbird had a similar problem. Clearing the cache fixed it for both of us.