During the last days I've completed quite long time challenge - make Weblate compatible with Python 3. It's probably still not in shape you would use it on production server, but it runs fine and the testsuite completes without errors.
As usual, the major obstacle are dependencies. The translate-toolkit doesn't support Python 3 in any released version, so you need latest Git snapshot. Another problematic bit is Mercurial, which will not support Python 3 in near future. But in case you need it, you can still install Python 2 version and use it from Weblate (it uses command line interface).
The porting was mostly dealing with encoding mess - in Python 2 you really didn't have to distinguish between binary and text data, while Python 3 quite enforces that. This turned out to be especially tricky with CSV files where csv module expects text streams in Python 3, while translate-toolkit CSV parser expects binary ones.
All this has one downside as well - the test matrix got bigger again, what makes the testsuite run longer with 5 workers available.
While doing these changes, I've also decided to drop support for Django 1.7, this will allow us to get rid of lot of deprecation warnings in Django 1.9 and prepare codebase for Django 1.10.