NEW DELHI—Reliance Industries said on Friday its low-cost 4G smartphone, jointly developed by the Indian group’s Jio telecoms venture and Alphabet’s Google, will launch in stores from this festive season of Diwali for 6,499 rupees ($87). The smartphone, the product of a $4.5 billion Google investment in Reliance’s digital unit last year, will cost 1,999 rupees upfront and users can pay the rest in monthly installments, Reliance said in a statement. The device comes with a tweaked Android operating system named Pragati, which means progress, and is aimed at first-time smartphone buyers with features such as quick translations in 10 Indian languages and a voice assistant which can read that text out loud from the screen. Google CEO Sundar Pichai said this week that the device partnership with Jio was about investing in local languages, other than English, so that many more Indians can use smartphones. “So I view it …