What programming language is the file.
A property that can be set to indicate what programming language the source file is. If it is not set the language is determined based on the file extension. Typical values are CXX (i.e. C++), C, CSharp, CUDA, Fortran, ISPC, and ASM. Setting this property for a file means this file will be compiled. Do not set this for headers or files that should not be compiled.
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https://cmake.org/cmake/help/v3.19/prop_sf/LANGUAGE.html