I'll translate it for you and edit this post when I've finished.
Edit: The double front brake allows to brake the front brake with the right and the left lever. On a technical point of view it's one cable (only one) that leaves the one lever passes the brake and comes back to the other lever. The cable will be measured closed. (Place one metal ball into the the lever and measure where the other side will be set on the other lever.) This method has got one disadvantage, you have to begin from scratch if you want to readjust or change your brake cable. (Overview/Photos 1 and 2)
Material: The pieces that come with the front brake. A Slick cable (Teflon).
A Oddysey Knarps or something like that.
This cable adjuster
it's generally set to the position you can see there.
Installation:
At first loose the screws that hold the brake cable.
Install the cable adjuster to your brake and the other thing you can see on the pic. (It's possible that's necessary to bore a bigger hole.)
Cut the sheath into 2 equal pieces. ( It avoids that you always have one lever that feels harder during brakings. )
Install the cable and one of the sheaths as you would install a single brake lever system ( consider that the cable hasn't been cut yet) Comment: The cable isn't blocked at all, only from the other lever.
It is there that that becomes complicated. The goal of the operation consists in tightening the cable and to place cable at the good place tightens it. Thus you have the sheath and the cable (which I recall it exceeded) in the right hand, slightly close again the jaw with your left hand (the way of which you will close again the jaw with your hand is decisive since it is with that that you will regulate the basic difference between the shoes and the rim). You can block the jaws in half-closed position using Scotch tape for example. To plate the sheath of brake against the thrust of cable with your left hand, tighten a little the brake cable which with completely had to slacken during all this time, maintain the sheath. During this time with your right hand, put the cable clamp on the cable, and try to judge for which level it would have to be tightened so that it returns in the hole of the lever which normally accomodates the small metal ball at the end of the brake cables (it is preferable that you leave a little bit of margin). When you think of having to find the place adequate tighten it (especially not à .fond for the moment!), so that it crushes a little the cable, ensure that the cable is nevertheless a tended minimum, that will avoid oneself tightening as nutcases the screws which tighten the cable on the levers, best would be to be to two, one which tend the cable and the other which places the cable clamp where it is necessary. Withdraw the cable clamp, you can stop maintaining the sheath with your left hand. Cross to the cutting pliers the cable approximately 2-3 mm after the mark made while tightening serves it cable (have good cutting pliers or your cable will be exhausted and it will not pass any more in the greenhouse cables). Give the cable clamp to the place of your mark, since you cut the cable after the mark the cable should not exceed cable clamp. You can tighten the cable clamp now well (it is a small screw allen which should be tightened, you will realize there once that you will have a cable clamp in hand). Attention, once tight the cable becomes almost a cable of single use, indeed it will be exhausted because of this tightening, therefore you do not mislead, leave a little margin rather when you carry out the mark quit to start again the operation several times by decreasing the margin.
Put the sheath and the cable correctly in the lever, and the turn is played.
The last part was translated with google, because i'm out of time. But i think google did good work this time. The other parts we're translated by me so i'm sorry if it's isn't accurate. :>