Part of the problem was that there is a lot less grammar in Chinese than in Indo-European languages. So there are many ways to translate a given Indo-European sentence into Chinese, and you need to understand context on a Chinese sentence to properly translate it into an Indo-European one.
The many ways to translate to Chinese is a problem because Chinese flexibility in word order means that there are many choices of reasonable next word, and they didn't have enough data to tell the difference between a reasonable next word and an unreasonable one.
Going the other way Chinese may not care whether you have one apple or 10 apples, or whether Xi is a man or a woman. But Indo-European languages generally do care. So Google Translate has to guess, and often gets it wrong.
Despite the documented failure modes (and they were many), suddenly it was possible to read articles in other languages, and it was likewise possible to make yourself understood in other languages using it. I personally know a lot of people who speak multiple of those languages. And they all agreed that it was a giant improvement. And the fact that it WAS a giant improvement was why they got rid of the previous translator.
I understand that it was terrible with Chinese. But I never used it for that.