I do my accounting in USD to make it more easy, so it's many currency but i still want to have the price in CDF on the bills and invoices I send to my customers

For pricing in other currency than company currency, use pricelists.

Hello AFRICAN TRADING GROUP,

Based on your provided details, your main company currency is DR Congo

This information is already available in the journal items tab:

let me know if I have answered your needs properly or if you mean something else