Thank you for the clarification. I had been taught the northern pronunciation for words of this type, so it is confusing and unsettling to hear the "shlesht" variant. And the similar hard/soft versions of Ich, etc. I really think Duo is doing us a disservice by mixing these up, and by being inconsistent also. As has been stated before, if this course was a beginning English course, I doubt they'd give "Hello" as hello and howdy and howyadoin and whazzup. And hi and hiya.
Why wrong with "The soup tastes bad" , I know schleckt means bad, but I thought its in the context of food taste.
There is no context of taste here.
The sentence simply says that the soup "is bad" -- whether that means that it's evil, or it's bad for your health, or it has gone rotten, or what, is not specified, but it's not (necessarily) about taste.