You definitely need to hire a lawyer. Even if you do so by telephone, send all your paperwork and let the lawyer give you actual advice.
The lawyer can tell you about the consequences of not dealing with this charge and the consequences to your immigration status if you do or do not respond. The lawyer can also tell you if there is any way that she or he can deal with the case in your absence. (I am not licensed in Wisconsin and you need to hire someone who is.)
Generally, it is not good to ignore these things and have a warrant out for your arrest. The lawyer can tell you about whether or not you are likely to be extradited based on the nature of the cahrge and the jurisdiction. But, even if you are not likely to be extradicted, getting the case resolved is your best bet.
So talk to a Wisconsin lawyer and good luck!
This is not legal advice. In order to get legal advice, you need to retain a lawyer and establish an attorney client relationship. So, talk to your lawyer!