Translation:The nation of Indonesia is a big nation.
Without context it is difficult to know exactly what is meant by "bangsa yang besar". Mungkin ini bisa menolong: "Bangsa Indonesia adalah bangsa yang berprestasi besar"?
"Indonesia nation" is not grammatical. You could say "Indonesian nation", but that puts a specific emphasis on the "indonesianness" of the nation that you may not want to convey. "Nation of Indonesia" is more neutral.