In a sense, any API that has its own functions and data structures becomes like a DSL. For example OpenGL feels like its own language, even when you write it in C or C++, or C#.
Moreover, in any nontrivial application, you have modules and layers of abstractions - and those boundaries are DSLs on their own. It's actually good to think of them as languages the client code will use to write its solutions in (SICP makes this point early in the book too).
People are getting too hung up on the word "language", like it was something only the most experienced and smartest of programmers were allowed to build. Nope, programmers build new languages daily in their code; it's how you abstract things.
