Corrected entry: In the original movie and in the sequel "Beneath", it is established the ape civilization has its own alphabet. However, the peace protesters attempting to block the Ape army from leaving Ape City have protest signs written in English.
Scott215
25th Jan 2015
Correction: Taylor spends a large part of the first movie communicating with Zira and Cornelius in written English. At no point is it established that the Apes have a different alphabet.