The translation machine answered as "The strawberry is popular fruit." Isn't indefinite article "a" necessary before "popular fruit"? In this case "fruit"means "a kind of fruit."
Yes, you need the indefinite article. The subject is “the strawberry,” a singular form referring to all strawberries collectively. You can also use “strawberries” in plural.
The strawberry is a popular fruit. Strawberries are popular fruits.