Can I and how to offer to translate papers (on COVID-19)? In light of the recent pandemic of COVID-19 spreading in the world, there have been many Chinese papers with only English abstracts published in Chinese journals. Some western papers have cited the Chinese papers, but only based on the abstract as the author would say they do not understand the Chinese full text. 

I am a graduate student in the medical field with a good grasp of Chinese and English. Can I translate without permission, or offer to translate, these papers and publish in an indexed English journal/source? If I make the offer, what is the appropriate etiquette and considerations?
At the scale of one person, you could do the following. If you find a paper that you think merits translation, contact the authors and offer your services directly to them. They might not be able to help much if their research is ongoing, but would, I think, respond positively. You could also suggest appropriate English language journals to them that might publish the translations. I can't predict how that would work, but archives might be appropriate. 

I think that a lot of researchers in China (as everywhere) have a working knowledge of English and so could probably vet any translations you do for accuracy. 

As for the etiquette, just ask, introducing yourself. Or even send along a sample translation of a part of a paper as a calling card. 

I don't think that copyright can be ignored unless governments intervene to change the rules. It might happen due to the seriousness of the issue. 

But being in contact with researchers who have been with this since the beginning might actually be an advantage to your career also.