Which logging library to use for cross-language (Java, C++, Python) system
I'd use Apache log4cxx or Apache log4j.
It's Efficient. It has Logger hierarchies to modularize your logs. It's proven tecnology for a  while now.
Currently, appenders exist for the console , files , GUI components, remote socket servers, NT Event Loggers , and remote UNIX Syslog daemons. It is also possible to log asynchronously.
How can I support distributed logging? 
With remote socket servers appenders for example.
I have a system where a central Java controller launches analysis processes, which may be written in C++, Java, or Python (mostly they are C++). All these processes currently run on the same server. What are you suggestions to

Create a central log to which all processes can write to
What if in the future I push some processes to another server. How can I support distributed logging?

Thanks!