Microservices are small independent services and loosely coupled. Each service is responsible for one business logic development.
If you are building an eCommerce system built on micro-services then it is possible that for API generation you are using PHP. But for notification and order generation you are using Node.js. Also for the search, you are using elastic.
It is not mandatory that the complete tech stack should be based on one server side technology. Unlike the monolithic system where the code base and stack is the same for all business services.