Prolog isn't dead, it's just resting. Actually, people find practical uses for it still though it tends to be domain specific.

Look at the alternatives. If there's a practical alternative to the language/material that has reasonably widespread use and can be counted on to be present in 5-20 years, go for the alternative. If you have a need for something that's been put through its paces for 40 years and is battle tested with well-supported compilers, consider the "dead language".

And you can always leave languages off your resume.