For purposes of filing your US income tax return, you can use your United States mailing address, or your could use your foreign address; although technically
speaking it really should not matter.
So, for the sake of simplicity, if
you still receive mail at your US address (and someone collects it there
for you), then you can safely use your US address on your tax return.
Otherwise, you can use your (temporary) overseas address. The main
purpose of providing the address information will be so that if the IRS
ever needs to contact you, they'll be able to write you a letter, send
you a notice, or mail you a tax refund. If that is more likely at your
US address than your Africa address, then chose the US address. If the reverse is true, then use your foreign address.
Thank you for asking this question, and good luck with your work.
