Specifically, I would like to know if their are age, skill or education requirements, and do you have to be fluent in the local language? Do embassys or consulates hire cleaning staff from the locality, or can Americans get that work? I am looking for an opportunity to work in Brazil, and not as an english teacher.

The previous answer is correct if you want to join the regular foreign service and be assigned anywhere. If you specifically want to work only at a low-level job in Brazil, you can apply through the human resources department at that embassy. You would need, however, to aleady have a valid work permit from the government of Brazil.

The skills required would vary by the job available. In most embassies, cleaning staff work for a contractor, not directly for the US government.

You'll find information about working for the US Foreign Service on the State Department website. Or you might be assigned as a specialist of another government department at the embassy such as the military.

Most embassies would hire local staff to do their cleaning depending on the cost of labour in the country.