IDE/GitHub - How can I switch it to the local repository

For SmartApps, you’ll need to host those yourself, and can use whatever language you’d like to communicate with the ST API.

For Device Type Handlers, it depends whether or not your device needs to connect via a Hub. For now, hub-connected devices are still using Groovy, with no replacement announced, yet… Direct-Connected devices will communicate directly to the ST Cloud Server via the new API.

There are threads discussing these topics, which are quite active with developers trying to migrate everything that they can.