Hi Leszek ,
Talend is a good tools and should work . but create and order from database is not a good approach.
User Intercompany feature and create a second org in the client A so you wil have the sales order.
Now you need only a process to send the order to a web services on the second client B for creating the sales order
(if you don't want to have 2 org in the same client as i suppose)
maybe should be other options...
Marco Longo
iDempiere Consulting