Well, if you read any of the already posted suggestions, you would see that three days ago, someone already requested this (yet again....). It can't be done because of how ATA designed the chat system.
Download any of the hundreds of OCR apps (optical character recognition), take a screen shot of the chat you want translate, and use the OCR app to convert the image to copyable text.
That take ages though 😂 there needs to be some way to make it easier to communicate with people speaking different languages