Afghanistan's constitution names Dari and Pashto as official languages. Dari, a form of Persian, is widely used as a common language, and estimates suggest about half the population speaks it. Pashto is spoken by roughly a third. Other languages carry official status in regions where most people speak them, including Uzbek, Turkmen, Baluchi, Nuristani and Pamiri languages. Many people speak more than one language, and literacy in any of them varies with the schooling a person was able to get.
The country is also ethnically diverse. The largest groups are usually listed as Pashtun, Tajik, Hazara and Uzbek, followed by Turkmen, Baloch, Aimaq, Nuristani and others. Treat any percentages you see with care. Afghanistan has not held a full census since the late nineteen-seventies, and a later count deliberately left out ethnicity and language questions because they were so politically charged. Religion is similar: nearly all Afghans are Muslim, most Sunni, with a Shia minority that includes many Hazara. Small Sikh and Hindu communities also have Afghan roots. Ethnicity, region and faith have shaped who was targeted in past conflicts, so these are not neutral topics for everyone.
For language access, the details matter. The Minnesota Department of Health notes that Dari and Farsi are both forms of Persian, but a Dari speaker may or may not understand Farsi well, depending on where they are from. MDH also recommends orienting interpreters to a family's city or province of origin. Less common languages among recent arrivals include Hazaragi and Uzbek. So do not stop at asking whether someone speaks Persian. Ask what language the person prefers, whether a particular dialect matters, and whether they want written material or spoken explanation.
Comfort with a particular interpreter can matter too. A person may prefer an interpreter of a certain gender, or may worry about confidentiality in a small community. Ask these questions of everyone, in a neutral way, rather than assuming what someone wants from their ethnicity or appearance. The person's answer is the guide, not your prediction.