Translation:The banks are not open on Saturdays.
Ups, I think you're right. I have checked online the schedule of several banks in Paris and now I see that they are open on Saturdays. I stand corrected. In the past I have lived in Paris for several short periods (I never really settled there) and I wasn't aware of that fact. I had always assumed it was the same way than in Spain. Actually it is funny because in general, opening hours tend to be shorter in France than in Spain.
The etymology seems to be wrong, see for instance here: https://en.wiktionary.org/wiki/laugardagr#Old_Norse