Pashto varies significantly by region. A speaker from Kandahar and a speaker from Nangarhar use different pronunciations and, in places, different vocabulary for the same everyday object. An interpreter who is fluent but unfamiliar with the speaker’s region will keep up and still miss detail.
Dari and Farsi are mutually intelligible but they are not identical. Vocabulary, formal register, and administrative terminology differ, and the differences show up exactly where they matter most, in official documents and legal proceedings.
Urdu carries its own registers, from conversational speech to the formal vocabulary used in legal and administrative documents. We ask which one the assignment calls for before we staff it.
So we ask where the speaker is from before we assign anyone. It is a short question at the start that prevents a long problem later.