é is converted to é (String), if you open the binary plist file in Xcode (or on an iOS device).

When I change the Type to Data it is listed as <c383c2a9>.

Logging entry and utf8 values in bplistCreator.js on line 226, gives: entry { type: 'string', value: 'é', id: 2 } utf8 <Buffer c3 a9>

According to http://utf8-chartable.de/ the UTF-8 code for é is c3 a9, which make up the first and last two characters of <c383c2a9>. The code in between 83 c2 makes two characters:
c383: Ã and c2a9: ©.