For example, Latin has been dead for a long time, but evolved into modern languages like Spanish, French and Italian. But in certain settings, people still speak Latin, like at Harvard commencement or in TV shows.
How do we know what it actually sounded like? Do we just assume that the characters we use today sound the same as they did 1500 years ago? How do we reconcile the fact that, for example, 'r' has a very different sound in French than Spanish?
I'd suggest also trying this question at r/askanthropology
Also Latin isn't dead. Catholic clergy and academics never stopped using it.
We discussed this exact question about 4 days ago here.