翻译High school is a difficult atmosphere,to put it mildly.

翻译High school is a difficult atmosphere,to put it mildly.
翻译High school is a difficult atmosphere,to put it mildly.

翻译High school is a difficult atmosphere,to put it mildly.
"to put it mildly” 是“说好听点”,“说的婉转些”的意思.和“不夸张的说”有些许差别吧……
整句：说的婉转点,中学的氛围令人难以忍受.

不夸张的说，中学的氛围很难熬