When will COVID19 become more widespread in developing countries (especially African continent)?

We can share the current data. According to WHO Global Statistics: 

• Nine new countries/territories/areas (African Region [7], European Region [1] and Region of Americas [1]) in have reported cases of COVID-19 in the past 24 hours. (Valid from March 16, 2020)
• A WHO high-level technical mission concluded a visit to Iraq to support the Iraqi Ministry of Health in their COVID-19 prevention and containment measures. WHO is working around the clock to establish 3 negative-pressure [contagious respiratory disease isolation] rooms in Baghdad, Erbil and Basra to accommodate patients who might require more sophisticated medical treatment

Link: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports/ 

According to WHO Africa:  

“As of 11 March 2020, a total of 47 confirmed COVID-19 cases, with no deaths, have been reported across nine countries in the region: Algeria (20), South Africa (13), Senegal (5), Nigeria (2), Cameroon (2), Burkina Faso (2), Cote d’Ivoire (1), Democratic Republic of the Congo (1), and Togo (1). Figures 1 and 2 show the temporal and geographical distribution of cases, respectively. In the rest of the African continent, a total of 66 confirmed COVID-19 cases were reported from three countries: Egypt (59), Tunisia (5), and Morocco (2)”  

Link: https://www.afro.who.int/health-topics/coronavirus-covid-19 

Another interesting source of information is Our World in Data which shows the location against how long it took for number of total confirmed cases to double.  

Link: https://ourworldindata.org/coronavirus