In France, the album debuted at number 8 in April 1988, but it dropped to number 26 five months later. However, thanks to the successful single "Pourvu quelles soient douces" (number-one hit in December 1988), the album reached number one for two weeks in December 1988. The album managed to stay for eleven months in the top ten and about one year on the chart. On 29 June 1988, the album was certified Gold by the Syndicat National de lÉdition Phonographique for 100,000 copies sold, then Platinum for 300,000 sales, then Double Platinum on 17 February 1989 for 600,000 sales, and eventually Diamond on 14 November 1989 for a minimum of 1,000,000 copies sold. The album was also released in Germany, where it reached number 47.
Question: What date did the album reach number 26 on the charts?
Answer: September 1988