I don't think you have to write your AI really twice. You are right, you have to look where you are (left or right site) but the most methods I write arn't concerned.
Most of my logic need to : am I in the right direction to shoot ? Is X behind/before Y ? So I have to change a lot of things for left side to right side. Well I have done a warper that translate the coordinates from right to left and now I don't have to deal with it. I have change the coordinates center too, I prefere when (0,0) is at the center of the field.
The dll problem: No, the linux and max user don't have to say "bye bye". But if you want to programm your ai in c++, you can do it (look at the tutorials) =) All the other persons can write their AI with java. I've tested it on mac and linux/solaris and it runs =)
There is only ".dll" no ".so", can Linux user test the C++ AI provided as is it ?
Nevertheless, my team is betting better

If I manage to do a good goal keeper, I think I will be able to beat all the provided team (Not so easy to do

)
I have download the "sound" version, beside the text to speech, there is not other sound ? If you put a sound when you shoot, there is a goal and a whistle at the begining/side change, the game will be far more lively.
How will the winner be decide ? Will it be the score in the "analyse" ? Or will you do elimination match ? (If I do it, I will do the analyse. Then keep the best 32/16 team depending of the number of participant. When I will do a elimination round a day

)
Last one (for today

), costum image can be used but it is an image for a team not an image by player ?