Below are the logging libraries that I've found for Pharo/Squeak:
Log4s for Pharo is a port of the VA Smalltalk port of the popular Java logging framework Log4j. I installed it from Pharo 5's catalog browser. 206 of 207 tests passed, with 1 failure. None of the classes is commented, although being a port of Log4j, the Java documentation should work as reference.
Nagare is a "flexible logger which connects to Fluentd." It was written to run on VisualWorks, Squeak and Pharo. I installed it from the catalog browser. None of the classes is commented. No test suite. Documentation remains on the Google Code project wiki.
OsmoSyslog is a "log backend/target to use system syslog." AGPLv3+. I stopped there.
Syslog is an RFC5452 Syslog UDP client. I installed it using a Gofer snippet. It loads OSProcess. Every class has a class comment. Test suite has four tests. Because I have OSSubprocess in the same image I did not attempt to run the tests.
SystemLogger "is an easy to use, very lightweight, and highly configurable object logging framework." It failed to install from the catalog browser but loaded successfully using a Gofer snippet. Every class has a class comment. 17 of 19 tests passed, with 2 failures.
Toothpick is a port to Pharo of the Smalltalk library written to run on Dolphin, Squeak, VisualAge and VisualWorks. Documentation on the original site looks good. 16 of 19 tests passed, with 1 failure and 2 errors.