Grading term papers and reports written by non-native speakers I'm teaching an advanced undergraduate computer science course that requires a 5-7 page term paper worth about 20% of the student's grade. 

The class has several international students, and some of them do not have a strong command of the English language. Clearly, these students are at a disadvantage when it comes to this assignment.

To complicate matters, the course is part of the university's "integrated writing" curriculum, so, according to university policy, the quality of the writing must be evaluated as part of the grading process. 

I'm trying to devise a fair scheme where non-native English speakers are not graded as stringently as native English speakers, yet not have the grading be so lenient for non-natives that it becomes unfair in the other direction. 

I've already decided that some criteria can be graded on equal footing (such as overall paper organization, and the quality of the overall research), while others (such as word selection and sentence structure) can be looked at on more of a two-tier scale. 

I'm wondering if anyone here as dealt with this dilemma before and, if so, how they might have approached this problem.
Grade everyone the same on things like word choice and sentence structure, but make that portion of the grade a small part of the overall grade for the paper.  (If you are in the United States, you will find students who are the product of U.S. high schools with limited vocabulary and no idea of sentence structure.)

Edit: If you don't grade everyone on the same scale, you will inevitably get complaints.  I'd argue that what is important (for learning) to students in your class is the formative feedback on their writing, not the specific number of points.  If the dean complains, 'splain that you teach computer science.

{Time passes} As Damian has said in the comments, you will need a grading rubric that assigns relatively low points to word choice and sentence structure, more points to overall organization, still more points to quality of research, etc.  Then you'll need to show how the overall grade was computed, using the rubric.  To repeat myself, the formative comments you make, particularly on word choice, sentence structure, etc. will be more important to learning than the actual points.