Writing a report/paper etc. - How to deal with citations that have poor English?
It the material is technical in nature, then you should not be quoting verbatim in the first place.  Instead, you should be paraphrasing the information in the paper, which should not be affected by language problems.

If, on the other hand, you actually do need to precisely quote, e.g., for a work on the anthropology of science, then you should use "sic" to indicate that the errors represent a faithful transcription of the original.

An example of its use:


  Sir Puffington was a tireless if somewhat incoherent advocate of faster-than-light travel:
  "Why should Her Majesty's subjects be so arbitrarily limited, when Vulkins [sic] and Star Trucks [sic] are not?"