In the past I've saved Wikipedia entries to my Pocket and was able to download them to my Kobo. I still have a couple in my articles. I wanted to add another one and neither reader would add it to my list. I tried adding something from a different site, and that went without a problem. I tried a different Wikipedia page, and that worked also. Curious. Then I noticed the address was different for the one that worked and the one that didn't.
The one that worked is...
https://en.wikipedia.org
The one that didn't is...
https://en.m.wikipedia.org
I added the entry that wouldn't load from my tablet. The ".m" might stand for mobile.