[pdpi]

Technical books aren't just about the code itself. Programmers don't necessarily make for good technical writers, and non-native speakers of any language are worse writers on average in that language. Put those two things together, and a non-native programmer writing their first book needs all the help they can get with editing and reviewing the text.

[arp242]

Even a native author will need all the help they can get with editing and reviewing the text. But yes, even more so for non-native speakers.