I used 5 randomly choosen english questions with easy answers my readers would know — this prevented literally 100% of the unwanted spam, while it was easy on the users.
If you want to filter comments you could even make the questions reflect the content of the article, filtering uninformed TL;DR type of comments and giving the users the feeling you value onformed opinions.
I once used a form with a random math question: 7+2 = __
It prevented 100% of bot spam for years. Granted, I was never a big enough target to make anyone rewrite their bot, but that's the same for most of us. I'd never use a captcha so long as something trivial like that works 100%.
If you want to filter comments you could even make the questions reflect the content of the article, filtering uninformed TL;DR type of comments and giving the users the feeling you value onformed opinions.