Will I need to learn Estonian to extend my researcher permit after five years?

Estonia has tied longer-term renewals to basic language integration. For residence permits for employment issued from 15 July 2018 onward, extending after five years of residence generally requires proof of Estonian at the A2 level.

A2 is a basic conversational level, lower than the B1 needed for permanent residence. If you expect to stay in research long term, it is worth starting language study early so the requirement does not delay your extension.