Problem building new language on opendatahandbook.org

Croatian team has translated opendatahandbook on Transifex. I’ve tried building sphinx but run into obsticles on my mac:

$ make html lang=hr
sphinx-build -b html -d build/doctrees -D language=hr source build/html/hr
make: sphinx-build: No such file or directory
make: *** [html] Error 1

Can somebody offer a help with building html for hr language?
all.po translation is available on Transfix and here: