A few points.  

 
 - As a reviewer,  I have often been frustrated by the quality of the English and requested that it be edited better.  It is hard to review papers with extremely poor grammar and it will be even harder as a published paper.  
 
 - That being said,  I totally sympathize with the problem of authors who aren't native English speakers!  I couldn't possibly write a paper in another language.  

So I think it is both fair and unfortunate to require English papers in English conferences to meet a minimal standard.  A fact of life.  

What can be done? 

 1. As someone commented,  it's a learned skill,  and your English skills improve over time. 
 2. You may have colleagues with better language skills who can help.  
 3. You can pay someone.
 4. Here's possibly a new idea,  or perhaps this is already done:  perhaps English speakers who have sympathy for non-English speakers without the financial resources can copy edit *pro bono*.  Someone would have to set up a site to play matchmaker. 
 5. *[EDITED to add an excellent comment and summarize it in the answer].*  Some universities and institutions offer proofreading services to their faculties: check if there is one in your home university. – *Massimo Ortolano*

I could see myself volunteering for such a task once in a while,  like a paper every month or two.  But I'm not prepared to support a site to automate the matches,  which would be necessary.  Maybe i can talk my teenager into doing it....