I think a good analogy might be that Google Translate is like someone who knows a target language well enough to translate fairly effectively most of the time, but still makes gross mistakes somewhat frequently. However, a listener fluent in the target language will almost always detect those mistakes: The listener may not know what the speaker intends, but will know that what was said in the target language makes little or no sense in the context, and can investigate to find out what was actually said or meant in the source language.
For example, "You can make book on that; it's a sure thing." --> Możesz zrobić książkę na ten temat; to pewna rzecz.
Google Translate has mistranslated two idiomatic phrases, but a Polish speaker is probably going to realize that something is wrong here and could investigate to find out what was intended.
Similarly, if I use Google Translate to translate, say, wiercić komuś dziurę w brzuchu
, and I get "to drill a hole in the stomach," it doesn't create misunderstanding. It simply becomes an occasion for investigation and further learning.
"a bet" (as in "I'll make book on that.")
By the way, "make book" refers to the bookie's side of the operation, not the action of the people who place the bets.
"When he makes his book on a race, he sets the odds on each runner so that the money he receives in bets should exceed the amount he will have to pay out whatever the result of the race."