What is the world's oldest language?

Sanskrit is the oldest language in the world, please see references below.

Vedic Sanskrit is the oldest attested language of the Indo-Iranian language family. It is the language of the Vedas, the oldest Shruti texts of Hinduism, compiled over the period of the mid 4th to mid 3rd millennium BCE. It can be said that Sanskrit, Greek, Latin, Tamazight, Hebrew and Tamil are the oldest major languages which are still spoken today.

Sanskrit was also suggested as the best language for use in Computational Linguistics and Artificial Intelligence by NASA. It is the only language in the world which is scientifically precise as was discovered by the NASA scientist Rick Briggs as published in the Artificial Intelligence Magazine
Rick Briggs:

"As we shall see, there was a language spoken among an ancient scientific community that has a deviation of zero. This language is Sanskrit."