The standard translation of "modern" to Chinese is "现代" (literally, "present time or epoch"). Unfortunately, Chinese (and possibly Japanese) historians and textbooks also have the word "近代" ("near epoch"), which, surprisingly, is usually translated as "modern" as well. According to Wikipedia, modern history began approximately in the 16th century, which falls into the 近代 (or even earlier, before 近代) in Chinese parlance, definitely not 现代. Since "modern" includes both what Chinese historians call 近代 and 现代, the whole of "modern history" should be properly translated as "近现代". But if the context limits the period to only part of the full span of modern history, "modern" should be translated as one of the two Chinese words, 近代 or 现代, depending on the context.
An obvious question to ask here is, Where is the division in timeline between 近代 and 现代? The Chinese Wikipedia page for "近代史" is made a counterpart for the English page for "Early modern period". So a natural answer is, Refer to whatever time the English phrase has the modern history divided by. Since early modern period is from 1500 (the end of Middle Ages) to 1800 (the age of Revolution, especially the French Revolution in 1789), that corresponds to 近代, and the period from 1800 on is naturally 现代.
But there're always different opinions. For example, according to the "近代史" Wikipedia page, the People's Republic of China traditionally takes 1640 (English Civil War) as the beginning and 1917 (Russia's October Revolution) as the end. But this tradition may be slowly going away as a result of academic globalization. Another page, for "中国近代史", states that "中国大陆的中国近代史学界基本确立从1840年“鸦片战争”到1949年“中华人民共和国成立”的分期方法" (the Chinese 近代史 scholars of the mainland China generally establish the chronological span of 1840 the "Opium War" to 1949 the "Establishment of the People's Republic of China" [as 近代]). The latter statement seems to be closer to what I remember. In that case, the generally accepted international standard of "early modern history" started way before the (mainland) Chinese historians' 近代, by more than three centuries, and ended about 150 years earlier!