Elsewhere on this website you will find This We Believe: A Statement of Belief of the WELS. The “Church and Ministry” section addresses your question on the basis of Scripture: “We believe that women may participate in offices and activities of the public ministry except where that work involves authority over men (1 Timothy 2:11,12). This means that women may not serve as pastors nor participate in assemblies of the church in ways that exercise authority over men (1 Corinthians 11:3; 14:33-35).” One of those assemblies is the voters’ assembly.
Do keep in mind that the relationship between women and voters’ assemblies does not speak to women’s status in God’s sight. Scripture says to Christians: “So in Christ Jesus you are all children of God through faith, for all of you who were baptized into Christ have clothed yourselves with Christ. There is neither Jew nor Gentile, neither slave nor free, nor is there male and female, for you are all one in Christ Jesus. If you belong to Christ, then you are Abraham’s seed, and heirs according to the promise.” (Galatians 3:26-29)
You may be interested in reading Male and Female in God’s World, a restatement of Scriptural Principles of Man and Woman Roles. The document will address your question in greater thoroughness than I can with this question and answer forum.