What is the language of the slogan of the Forum on China-Africa Cooperation?

It’s French

“The inspection team saw that the environmental layout work was basically ready, and the nine electronic display screens at the gate and in the park were in Chinese, English and French. The text hangs and displays the welcome slogan about the Forum on China-Africa Cooperation"

Africa was once a French colony

So now many Africans speak French

At the end of the 19th century , along with the rapid expansion of French colonies, the concept of "French Country" also came into being.

French has considerable influence in Africa. Since many places were French colonies in the past, most of these countries (probably more than 20) still use French as their official language after independence.