Zhang Shenfu (Chinese: 张申府; 1893–1986) was a founder and quitter of the Chinese Communist Party, a philosopher, and a political activist.
There are some fragments of evidence in the book Time for Telling Truth is Running Out: Conversations with Zhang Shenfu. In the introduction, Vera Schwarcz describes her visit to a certain room in Zhang's house:
My eyes roam over American, German, French, English and Japanese journals from the 1930s.
So that implies four languages that he may have at least read, in addition presumably to Mandarin. Elsewhere the book makes clear that Zhang spent time in France and Germany, increasing the likelihood that he might have not only read but actually spoken those languages.
EDIT: Thanks to user2448131, I'll add a key quote from the same book:
A voracious reader, Zhang Shengfu has unlimited access to the foreign language periodicals in the library [at Beijing University]. [...] By 1918 Zhang can read English, French and German. He is also teaching himself Japanese, Russian and Polish [...]
So this gives us an upper estimate of seven languages, including Mandarin, of which Zhang at least had some basic working knowledge. As for actually speaking though, the number is likely to be smaller.