The ubuntu package relies on an external lua interpreter, i.e. the lua5.3 package. The only binary built with the internal lua interpreter enabled is windows, AFAIK.
When compiling darktable, on linux, the build process searches for a lua installation and uses that, if found. You can change the CMakeLists.txt file and enable the internal lua interpreter, which will cause it to get built into the binary.
I’m running ubuntu 18.04. I installed the lua5.3 package using apt-get. I installed darktable from Pascal’s PPA. The lua scripts work fine.
I’ve also downloaded the latest git and compiled it. It builds with lua support enabled automatically and, again, lua scripts work fine.