Hello Christophe,

In v9 or v10 You can't directly import account move lines as you can't directly create an account move line.

To import account move lines, I suggest you import them as part of an account.move

In your .csv file you can add columns with line_ids/ in front of your account.move.line columns name 

Make sure that debit and credit (sum of all your lines) are balanced otherwise it won't allow you to import it.