This article from The Scientist is right that language problems aren't always what get international authors' research manuscripts rejected by English-language science journals. Most often, there is a problem with the research described in the manuscript. But still, even though many journals will say publicly that poor English won't cause rejection, authors and editors alike know that's not always the truth.
Sometimes the problem is cultural differences between authors and the staff of target journals. If authors are unfamiliar with how a journal's publishing culture operates, they can lose chances to get published. If, on top of that, they are not native speakers of English, there can be rejection-inducing misunderstandings in communication. And finally, some journals' peer reviewers truly will not even review a manuscript if they can tell that English is not the authors' native language.
When authors who are non-native speakers of English look for editors outside their target journals to help them, they may encounter some editors
- Who aren't highly skilled and thus who introduce errors into manuscripts
- Who are in financial relationships with the journals and thus don't have the authors' best interests at heart
- Who aren't willing or able to help authors understand the journals' culture
- Who fit all of the preceding descriptions.
It can take time, but authors can eventually find editors like me who are quite skilled, who have no financial connections with the authors' target journals, and who are happy to “translate” the culture of authors' target journals. And once they find such editors, they can build long-term work relationships that benefit both parties.
Authors who want more information on working with good editors should read the book Editing Research: The Author Editing Approach to Providing Effective Support to Writers of Research Papers, by Valerie Matarese. [Disclosure: I am one of the expert authors quoted in the book.]