Is it an ethical practice to offer co-authorship on a paper to a graduate student in exchange for proofreading the paper? By proofreading, I mean fixing small grammatical or spelling errors right before manuscript submission, not contributing significant comments to the experimental design or methodology that are later taken into account.
I ask because in my old lab we had several international students and several fluent English speaking grad students, and the fluent English speakers are listed as co-authors on several papers where they have contributed nothing more than small grammar corrections.