Deuteronomy 17:15, 18
15 you shall surely set a king over you whom the LORD your God chooses, {one} from among your countrymen you shall set as king over yourselves; you may not put a foreigner over yourselves who is not your countryman.
18 "Now it shall come about when he sits on the throne of his kingdom, he shall write for himself a copy of this law on a scroll in the presence of the Levitical priests. 19 "And it shall be with him, and he shall read it all the days of his life, that he may learn to fear the LORD his God, by carefully observing all the words of this law and these statutes, 20 that his heart may not be lifted up above his countrymen and that he may not turn aside from the commandment, to the right or the left; in order that he and his sons may continue long in his kingdom in the midst of Israel. (NAS)
And he writes for himself a Torah scroll - the Gemara explains that the king is obliged to write for himself two Torah scrolls, as it is written, "that he shall write him two of this Torah"
(Deut. 17:18 according to Rashi) - Every person in Israel is obliged to write for himself one Torah scroll, as it is written, "Now therefore write you this song for you" (Deut. 31:19)
Midrash by Moishe Horowitz,
Since the scripture says, "and YOU shall WRITE ... on the door post of your house and on your gate ...",
The Hebrew, "vu'ketavetam al-mezzuzot bieteka vu'bishe'arei'kah" has the connotation of the person personally writing this parasha on his own mezzuzot (door post) and his gate.
One would think the father should write this in front of his children. It would encourage closeness in the family. It would fulfil , "you shall teach your children", it would give inner strength and stability to the children.
Also, even though Hebrew is the popular language in Shul, what is wrong with writing the message for mezuzah in your native tongue?
This practice of mezuzah, would be more of a reminder (as one passes by the mezuzah) if the scroll inside had been written by the husband/father in the presence of the entire family and then placed in the holder for Chanukkat Ha-Bayit.