I once sent a paper authored by a Chinese scientist to a highly-qualified English-speaking reviewer in Greece. The English was somewhat problematic, but I thought it might be good enough for review. The reviewer returned it saying he could hardly understand the English at all.
This true story illustrates why we are so insistent upon authors using standard English. The problem, ironically, is that English is a second language for many of our readers and reviewers. I grew up in New York hearing all kinds of accents and syntactical variations of English and became pretty good at parsing non-standard grammar. However, if you’re already struggling to deal with English syntax, text that breaks the rules likely will be very confusing.
It is unfair to ask reviewers to review a paper in a language they cannot fully understand. Therefore, one of my initial screening criteria is language. If your English skills are weak, the best thing you can do to improve your chances of getting your paper into review is to have it reviewed by a good English editor BEFORE submitting it.