Accrue interest every 15 days/half month (1st to 15th, and 16th to End Of Month, i.e. 28th, 29th, 30th, or 31st), called the French ‘quinzaine’ process.
The application frequency could be at a different interval, however, and this request concerns accrual frequency only, not application.
For example, with an interest rate of 1.5% per year of 365 days, and interest applied every year (on the 1st of January):
This is a common banking practice in France, and followed by many organisations there.
Links (in French):
https://www.cbanque.com/placement/livret.php#plSHmctViZlbIh2G.99 (Here there is mention of a year split into 24 x 2 weeks, as well as the scenario described above, namely 1st to 15th of every month, and then 16th to end of the month).