and it is also the language of Cabo Verde, Guinea, Sao Tome and Principe, Angola and Mozambique. it is also still spoken in the State of GOA in INDIA. and a little in the now Chinese city of MACAO. . Altogether some 270 millions people.
It is portugheza, because it is a noun (meaning the Portuguese language). Portugheză is the adjective, so than the word "limba" has to be there too.
You can use: "limba portugheză" or just "portugheza" .
I think the best comparison is in this exact sentence, "limba Portugaliei" versus "a Braziliei", and the explanation is that for "Braziliei" you don't repeat the noun "limba" therefore you substitute it with the "a".