Supposedly Latvian and Lithuanian are the closest living, spoken, languages to Sanskrit. This likely reflects the fact that Sanskrit being that it is not spoken doesn't evolve and Lithuanian and Latvian have changed the least among living Indo-European languages.

https://www.news9live.com/art-culture/why-lithuanian-sanskrit-similarities-continue-to-intrigue-linguists-two-centuries-on-158492

https://www.reddit.com/r/linguistics/comments/aqjegs/connections_between_lithuanian_sanskrit/