- You can use any language (that provides a mechanism for creating libraries) to build a framework.
- Learn the language and development platform of choice, first. Creating a framework is just creating a library that provides a useful foundation for people.
Just trying to "Set out to build a framework" is probably not going to be too successful, however. Typically, a successful project, especially one being done for fun, is one that fills some need... Think about what you are developing, or what you want to develop. Create a project that is exciting, fun, and useful for you.
If, in the process, your project gets large, you can always pull out the building blocks and turn it into a framework for other people to use, as well.