Does the husband's taking of some items from the embassy that has closed—including a wireless internet device registered in the name of the embassy—count as theft, and what should the wife do about it?

This device belongs to the state, and it is not permissible for your husband to take it without the permission of the competent authorities. Otherwise, it would be considered consuming public funds unlawfully. The Prophet, peace and blessings be upon him, said: "Indeed, there are men who delve into the wealth of Allah without right, and for them is the Fire on the Day of Resurrection." Therefore, he must return it to the state, as this is part of fulfilling the trusts that Allah has commanded, as He said: "Indeed, Allah commands you to render trusts to whom they are due." As for whether it is theft, that depends on its conditions. Your duty towards your husband is to advise him, instill in him the fear of Allah, and strive to return the device or its value to the state in a safe manner.