I believe it means that the French economy has contracted, or become smaller, twice recently. Literally a double dip is an ice cream cone with two scoops of ice cream, so describing something as a double dip, means it was done twice. In this case 'spell' means signifies, or indicates.

A "double dip recession" (or contraction) is an economics term, it means the economy suffered a contraction/recession, recovered for a short time, and then fell again.