Sometimes there are situations where a man feels called to the mission field, but his wife doesn't, but they go anyhow because the wife wants to be submissive to her husband. While this is admirable, it is unwise. Moving overseas is a huge commitment, and a huge lifestyle change for the whole family. It is totally unlike staying in your home country where family life might look similar regardless of whether the husband is a pastor or businessman or plumber.
It is unwise for a couple to go to the mission field thinking that only the husband is the missionary. Both husband and wife must think of themselves as missionaries, and be committed to the calling that God has placed on their lives together. In cases where the wife merely follows on the husband’s coat tails, these couples don't last long on the mission field. The wife often ends up resentful of having to do something she really didn't want to do to begin with. Unless you are convinced that God has called you to the mission field, the stress from living in another language and culture (FAR from family back home) is too much to endure. Men, if you want to be a missionary, make sure you take the necessary time, together with your wife, to pray and talk about it and discern together if God is calling you as a family to go. And if your wife is not on board 100%, don’t go.
With that said, the role of the wife on the field varies from family to family. For some couples, the husband is the one doing outside the home ministry, and the wife is mostly at home with the kids. For other couples (who don't have kids, or whose kids are grown), both husband and wife are active in outside-the-home ministry. For other couples (such as my wife and I), the husband does the bulk of outside the home ministry, but the wife disciples some women and shares the Gospel as she is able.
The fact that both my wife and I see ourselves as missionaries doesn’t mean that we have exactly the same roles. And those roles may change over time as our kids grow up. During this stage of life when we have small kids, my wife is largely at home with the kids, homeschooling, etc. Last term when we were doing church planting up country, I would sometimes be with the kids so my wife could go out and visit some ladies to study the Bible, pray, and disciple them. When our kids our grown, the situation will change yet again. Each couple needs to decide for themselves what the role of the wife will be, but both spouses need to be totally invested in what God has called the family to do, even though roles will differ depending on gifting, time, ability, and stage of life.
And at the end of the day, some couples discover that the people around them learned just as much (if not more) about God from watching their family life and how they raised their kids, as they did through what was taught. Teaching the Word of God should never be neglected, but at the same time we cannot underestimate the importance of wives and mothers in reflecting the glory of God on the mission field, both inside and outside the home.