In a large bowl, whisk milk, pineapple juice, chili-garlic sauce, lime juice, brown sugar, garlic, soy sauce, and ginger until well combined. Add chicken and toss to coat. Cover and refrigerate at least 20 minutes or up to 4 hours.
Remove chicken from marinade and transfer to a baking sheet, letting excess marinade drip back into bowl; season chicken all over with 3/4 teaspoon salt. Reserve marinade.
Prepare a grill for medium-high heat; preheat 5 minutes. (Alternatively, use a grill pan.) Lightly brush grates with oil.
Meanwhile, transfer marinade to a medium saucepan and bring to a boil over medium-high heat. Continue to boil, stirring occasionally, until marinade is thickened, about 5 minutes. Remove from heat.
Grill chicken and pineapple, turning once, until chicken is lightly charred in places and an instant-read thermometer inserted into thickest part of chicken registers 165° and pineapple is tender and lightly charred, 8 to 10 minutes.
Transfer pineapple and chicken to a platter, drizzle with sauce, and sprinkle with cilantro.