As for French, it is used in many countries. However, except for several European countries such as France, most of them are practical (and some of my classmates have asked some Africans that they speak English instead of French now), so the books that can be read after learning French are mainly French books published in France. But French also has the same problem as English mentioned above, that is, it is impossible to read ancient books. In recent years, the largest proportion of foreign books imported from China is English writing, while French books are relatively rare in the market. So it will be very troublesome for you to find the source of the book. At present, I really haven't seen China introduce a French book published by an African country.
Although the status of Chinese is getting lower and lower in our country, we have to admit that Chinese has two advantages that English, French and other phonetic symbols do not have: connecting dialects and connecting ancient and modern times. Although it is difficult for modern people to read classical Chinese, it is not a big problem to get an annotated dictionary of ancient Chinese. So if you study Chinese, you can look at works from different eras. China has thousands of years of civilization, and there are still a lot of books to read.
If you have to speak a foreign language, English is the first choice. But according to your question, you should be looking for a foreign language other than English. Then I recommend Japanese. I think Japanese is less difficult for China people to learn than English and French. Moreover, Japanese books that can be found on the Internet, Japanese learning publications issued in China, Japanese dramas, cartoons and other resources are still relatively rich. Learning some Japanese ancient books can even help us understand the ancient culture of China.