César didn't 'win'
Great film. I felt very strongly at the end that César ultimately hadn't 'won', and wanted to make my first IMDb comment about it.
Clara was seen throughout the film as a positive, energetic person, capable of putting a positive spin on most things, even treating the bug infestation as a opportunity to have a spring clean.
At the end of the film, we see a relaxed and happy looking Clara before she is called by her mother to collect her letter. The fact that the first thing she does is hold the baby closely after she finds out the truth, rather than moving away from the baby or shunning it, shows what kind of person she is. I reckon she'll love the kid regardless of his or her heritage and be able to move on and separate César from the child in her arms.
César thinks he's condemned Clara to a relentlessly miserable life, where baby is a constant reminder of what awful things happened, but I think he's wrong. His being arrested and sentenced will give Clara the closure and safety she needs to pick up and carry on. That's not to say it won't hurt like hell and be tough for a while, of course, but I just don't think she'll become evil, hateful mum who ends up alone.