Should we vote down a question because of bad English? How much effort should we have to put in to understand a question?
In my opinion, downvotes should be used as a last resort. I've not always followed this rule myself in the past, but I've come to realize that some questions and answers can be salvaged with a simple follow-up comment.
You might try asking the OP (original poster) to clarify his or her question/answer if there is something you don't understand. Take a look at the question. I left a comment as an example.
As another option, if you can understand what is being said but there are lots of typos, you might consider suggesting an edit by clicking on the
edit link under the question/answer.
Until you get 1000 reputation, you can actually gain 2 reputation points if the OP accepts your suggested edit. Not only does this benefit you, but it benefits the OP if the question/answer is upvoted, and it benefits the community as a whole by helping to create really great content.
Both of these techniques demonstrate positive re-enforcement. The more of this re-enforcement we give community members, the stronger this site will become, and the more likely it will be to succeed.
Of course, down-voting a question/answer that you disagree with, that you're sure can't be improved, is something that you are free to do.
I will definitely down vote a question if the English or grammar is so poor that it makes it difficult to discern what is even being asked. Obviously if I can think of a way to make it better I'll suggest an edit, or barring that I'll post a comment asking the original poster to clarify.
That said, I think the down vote provides the right motivation for the poster to improve their question, and once they've edited it the site will let you change your vote.
This is exactly how the system is suppose to work. Good questions are up-voted and bad ones down-voted. If someone wants more votes for their question and people have left comments suggesting improvements they either make a change or see their question buried in the weeds.