irrévocablement

07:49 Mar 16, 2012 

What do you think of this?
I hereby irrevocably subscribe for twenty thousand (20,000) class "A" shares in the XXX. company, at a unit price of one hundred (100) euros per share.
In addition to my subscription, I hereby undertake to irrevocably transfer the sum of two million (2,000,000) euros to the bank account of same Company this day, the date of signature of this share subscription form.

07:14 Mar 16, 2012 

Further to my comment in agreement with Sangro's suggested answer, I would like to emphasise that the original is actually giving effect to the subscription. It confirms the subscirption.

Note that the transfer of funds however takes place at some time later that day. There you could consider that you have an undertaking to do something at some future moment in time. Again, though, you will note that the transfer is to be irrevocable.

"Je déclare souscrire..." could run something along the lines of "I hereby certify subscribing irrevocably for twenty thousand Class "A" shares...". Or, "I hereby certify my irrevocable subscription for ...".

As for "en complément de ma souscription .... sera irrévocablement transférée...", this is with reference to a future event. None the less, it remains irrevocable.
"In addition to my subscription, I hereby give my undertaking that the sum of ... will be transferred irrevocably...". Or "I undertake to make an irrevocable transfer of funds in the sum of ...". Note that "irrévocablement" refers to the verb "transférer".