Writing a report/paper etc. - How to deal with citations that have poor English? I've tried looking for suggestions on the internet to my question but haven't found any useful information.

I'm writing a paper and I'm quoting/citing various books, journals etc. However, I'm coming across of papers that are relevant to my paper that I would like to take quotes from, but were either originally written in another language and have been poorly translated, or were written with bad English to begin with.

Can I quote/cite the papers with corrected English or put the quote as-is? I'm worried if I don't correct the spelling mistakes/poor grammar etc. that the reputation/validity of my paper will be impacted. On the other hand I don't want any corrections I make in the quotes to be considered plagiarism. What should I do?

Edit: I'm writing a literature review section for the paper, if that is relevant.
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?"