First, often there's a local, state, and international language. This is endemic in India but also exists elsewhere. In Barcelona for instance, there's Catalan, Spanish, and English.
The migrants to Barcelona generally know at least one of these; such as Turkish and Catalan, or Arabic and Spanish. So what do you display? The Catalan version? Spanish? English?
You can find the differently-scoped languages in unlikely places; in Mexico for instance, Nahuatl has 1.4 million speakers and Yucatec has 759,000. That's about the population of San Francisco. Not a small number.
Second, international migration is only slated to increase. In Los Angeles, the neighborhoods of say Huntington Park (pop 58,800) and South Gate (pop 95,677) are 97.1% and 94.8% Hispanic/Latino respectively while Monterey Park (pop 61,085) is 86.3% Asian/Pacific Islander. The Burbank/Glendale area has the largest population of Armenians outside of Armenia. Over 50% of LA residents don't speak English in the home.
So for these cases, is defaulting to the state language a better user experience than fixing the language selection process?