"Simple made easy" [0] by Rich Hickey is a must-watch (even if you never touch Clojure)

[0] https://www.youtube.com/watch?v=SxdOUGdseq4

All talks by Bret Victor are great, they are listed on his websites but they are more concerned with the future of programming than old languages: http://worrydream.com/

On the topic of language design, there is also this talk by Brian Kernighan which gives good practical advice if you're building a language and talks about his journey with awk: https://www.youtube.com/watch?v=Sg4U4r_AgJU

Stop Writing Dead Programs