Is it legal for an intern to go to shanghai on A L visa for slightly less than 3 months?

If you go to Shanghai as an intern, you should apply for a F business visa in fact. If you conceal your travel purpose to China and study/work as an intern in China, you maybe punished once found by the local public security bureau or by the immigration office when you exit China.

I understand that there are risks. But do you have any idea as to how they could possibly find out?

If you will stay in China for over one month, you may be required to apply for a residence permit at the local public security bureau. Meanwhile, a tourist visa will not be granted with a duratiion of over 30 days usually. To apply for a China tourist visa, you have to provide your travel itinerary in China. Any fault info. filled in the visa application form may lead to visa rejection by the embassy.

Hi Angela, if you intended to so, please think about it carefully.