It depends completely on how you want to go about studying Chinese history and how much of an investment you're willing to make into learning a very challenging but very rewarding language.

There are more than enough quality secondary sources and translated primary sources for someone to get a general understanding of Chinese history for their own enjoyment. That being said, the volume of untranslated primary sources is absolutely massive, and since many professional historians are bilingual much Chinese-language scholarship remains untranslated. If you intend to study any particular period or aspect of Chinese history in depth, then language ability will greatly improve your ability to learn and understand your subject.

There's also a separate debate about the usefulness and accuracy of translation, even when done by skilled and knowledgeable translators. The major structural and lexical differences between Literary Chinese and English means that, inevitably, something gets lost, added or changed in the translation process. This won't be a serious problem for a leisure reader, but when looking at a text in depth there's only so far you can go without reading the original.

It also bears pointing out that while contemporary Chinese scholarship is written in the vernacular, the great majority of pre-20th century material is written in Classical or Literary Chinese, which differs significantly from the vernacular form. This raises another question, which form of the language you'll focus on as you study (and, if you intend to learn to speak it as well, which modern dialect).