I have heard this question in my home on more than a few occasions.  In my Grammar with guys post I shared my struggles with trying to convey why learning grammar is important.  But I want to share with you an inspiring story I found that might be helpful in this area.  I work part time at a home for the elderly and one of the activities we like to do is read aloud.  Right now, we are reading "In My Father's House" by Corrie Ten Boom.  When I read this portion of chapter 6, I could not help but think of my children's question "when are we ever going to use this?" . . .

Bible Study Was a Game
     With the dishes cleared off and kitchen duties accomplished, the oval table could be turned into a place for games.  We didn't play cards (for that was considered a form of gambling), but we had a lasting enjoyment in the type of games which taught us something.
     Different languages were introduced as a game, not as a forced study.  When I was in the fourth grade, we began to learn French.  As I remember, I loved the melodious sounds of this beautiful language, but it was and remained a difficult language for me.  The next year I started English, which was easier but I wondered as I struggled with all the different English meanings for words if I would ever go to England or America and have an opportunity to use the language.
     Father wanted me to learn English well, and he gave me a little Sunday-school booklet in English which was called "There's No Place Like Home."  I read it over and over again.
     The greatest fun in language-learning came during our Bible study.  The entire family would take part, each one of us having a Bible in a different language.  Willem usually had the original in Hebrew and Greek; I would have the English; Mother the Dutch; Nollie the French; and Betsie or Father, German.  It was a special and joyous time for us.
     Father would begin by asking what John 3:16 was in English.  I would answer from my English Bible, Mother from her Dutch Bible, and Betsie would reply in German (and so on).
     When I was so young, it didn't seem possible that Betsie would ever have a chance to use a Bible verse in German.  We didn't know Germans then!  However, God uses such seemingly insignificant ways to prepare us for the plan He has for our lives.

These girls could have never known the events that would take place some 40 years later.  Before being taken away to their concentration camp, one of Corrie's relatives managed to smuggle a small Dutch Bible to her.  In the evenings in their barrack room, Corrie and Betsie would read that little Dutch Bible.  The women who shared the barracks with them were from many countries including Poland, France, Germany, and Russia.  Corrie and Betsie translated their Dutch Bible into German.  Then someone else translated the German into Polish, and so on.  Just like her family used to do around their dinner table all those years ago. 
Reading in a different language was difficult and frustrating for the girls when they were young.  But sitting in that barrack, under those terrible conditions, sharing the message of God's love that brought all of them comfort, I am sure Corrie and Betsie were so thankful that God had stirred their father to make them learn to read their Bible in German.  He obviously made learning fun, and somehing the whole family did together.
I am so thankful that I found this story.  There are many day to day tasks that we do that seem meaningless.  But God in his sovereignty will lead us to stick with those things that will later help us fulfill His plan and purpose for our lives.  And yes, that probably even includes those sometimes unpleasant tasks like learning a language and grammar!