Here in Germany we only have flat fines for standard traffic infractions. If you make it all the way into crime territory we have the concept of Tagessätze (lit. day fines). The court sentences you to X amount of Tagessätze. The actual fine per day is determined based on your income, usually equal to the amount you make after taxes per day. The judge is free to either estimate your income or can require you to declare it.
There is something similar in France : "jours amende". The key point is that if you don't pay the fine, you go to prison the number of days indicated in the "jours amende". It's for criminal court, not for traffic infractions.
