Written from right to left, old Indonesian language (6)
I believe the answer is:
navajo
'language' is the definition.
(Navajo is an example)
'written from right to left old indonesian' is the wordplay.
'written from right to left' says the letters should be written backwards.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'indonesian' becomes 'javan' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'o'+'javan'='ojavan'
'ojavan' backwards is 'NAVAJO'.
Can you help me to learn more?
(Other definitions for navajo that I've seen before include "Native American from Arizona, New Mexico or Utah" , "A N. American Indian people" , "Native American - on Java (anag)" , "N American Indian tribe" , "A native American Indian people" .)