Hi SIEWE TIENTCHEU Marcelin,

W.r.t your query I have gone through your query and tried to replicate it. Few recommendations which I would like to suggest you based on your query are :-

1) Firstly, its possible to populate Taxes, while adding a Sales Order Lines in Odoo by default through configuration

2) To have this feature following steps can be followed :-

    i) Go to Product creation page by following Sales>Products>Products

    ii) Here, under the tab Accounting, there is a field Customer Taxes

  iii) Here we can add the taxes which are present by default in Odoo or we can configure/create a new Tax as per our         requirement

   iv) Now after Configuring and Saving this configuration we would be able to have taxes automatically added for that particular product for any Customer.

For E.g. If I have a Product P1 and while configuring the product I have added any of the taxes in the field “Customer Taxes”. Now while creating a Sales Order, when ever we add this Product P1, for any Customer, taxes would be automatically populated against this product.

Hope it helps!

Cheers.