[isidor3]

Yes, Lua was originally written as a language for rich configuration files and has grown out of that into a more fully featured language.

It's also one of the easier languages to sandbox, since you can evaluate user provided code in a custom environment that only contains the functions you deem safe. You can even use the standard debug hooks to set an upper limit on the number of instructions a script can execute to prevent someone from creating an infinite loop in a config file and locking whatever thread is reading the config.

It's not very appropriate as a data serialization format, or as machine written config, but the parent post specifically asked about human written configuration files.