CMake/Help/command/enable_language.rst

enable_language
---------------

Enable languages (CXX/C/OBJC/OBJCXX/Fortran/etc)

.. code-block:: cmake

  enable_language(<lang>... [OPTIONAL])

Enables support for the named languages in CMake.  This is the same as
the :command:`project` command but does not create any of the extra
variables that are created by the project command.

.. include:: SUPPORTED_LANGUAGES.txt

This command must be called in file scope, not in a function call.
Furthermore, it must be called in the highest directory common to all
targets using the named language directly for compiling sources or
indirectly through link dependencies.  It is simplest to enable all
needed languages in the top-level directory of a project.

The ``OPTIONAL`` keyword is a placeholder for future implementation and
does not currently work. Instead you can use the :module:`CheckLanguage`
module to verify support before enabling.