The persian that is spoken in afghanistan is older than the kind spoken in Iran.
Known in English as Dari, in Dari it's called (drum roll please)... "Farsi."
These are interesting articles on the significance of seemingly meaningless linguistic matters. Returning always to the point: "words have meaning."
I generally oppose the idea that we should, in English, always defer to the local language for foreign items or names for which we have a perfectly functional word in English. Imagine if we suddenly began calling Germany "Deutschland" instead of the name we have long known it by, a name derived from Latin "Germania".
Next they'll be wanting us to learn Maori to talk to New Zealanders. Enough, says I.
d.o.l.
Criminal Number 18F