The relationship is as follows: Muhammad said that the Koran should be read in Arabic and in Arabic only, that all translations are not the word of Allah, because Allah was speaking Arabic when he spoke to Mohammad.
So in theory, all Muslims memorize the Koran in Arabic. That is one of the major duties of a madrassa: to teach the memorization of the Koran in Arabic.
Suppose you had memorized the entire King James version of the Bible in English. How well , one might ask, would you be able to speak and understand the English of King James' time?
The language it is written in is Arabic, and it is recited in Arabic in Madrassas.
So in theory, all Muslims understand Koranic, called Classical, Arabic.
Afghans speak a variety of languages, but more speak Pashtoon (Pashto) than any other. The other official language is Dari, or Persian (Farsi), also spoken in Iran and Tajikistan.
They also speak Uzbek, Turkmen, and Balochi.
Obama is correct in that the US has far too few speakers of ther places where our soldiers are sent.