This is a law issuing from the British government—the British North America Act (known since 1982 as the Constitution Act, 1867)—that created the "Canadian Confederation." In 1867 Canada comprised only four provinces: Ontario, Quebec, New Brunswick, and Nova Scotia.
The Constitution Act, 1867 contains just one section regarding linguistic matters, section 133, which stipulates that all legislature members have the right to use either English or French in the Parliament of Canada and the Legislature of Quebec. In addition, citizens can use either of the two languages in any pleading brought before the federal courts of Canada and all courts of Quebec. The wording of section 133 is as follows:
1) Either the English or the French language may be used by any person in the debates of the houses of the Parliament of Canada and of the houses of the Legislature of Quebec; and both those languages shall be used in the respective records and journals of those houses; and either of those languages may be used by any person or in any pleading or process in or issuing from any court of Canada established under this act, and in or from all or any of the courts of Quebec.
2) The acts of the Parliament of Canada and of the Legislature of Quebec shall be printed and published in both those languages.
Of course, section 133 did not officially establish bilingualism throughout Canada; rather, it simply made it possible to use English and French in the federal Parliament, the Legislature of Quebec, the courts in the province of Quebec, and the federal courts. Moreover, the Constitution Act, 1867 committed neither the federal government nor the public service under its jurisdiction to bilingualism. It was simply the "beginnings of official bilingualism." Section 133 remains in effect today.
Section 23 of the Manitoba Act, 1870 (equivalent to a constitutional law in this case) contains a provision similar to section 133 and grants Franco-Manitobans the same linguistic "rights."
In the judgment Attorney General of Quebec v. Blaikie (1981), the Supreme Court of Canada elaborated on a previous decision (1979), ruling that the requirements of section 133 apply to legislative texts adopted by the government or subject to the approval of the government, a minister, or a group of ministers. This is why the Constitution of Canada, as interpreted by the Supreme Court of Canada since 1979, requires that legislative texts, such as regulations and orders of a legislative nature, be "established," printed, and published in both official languages. A legislative text is "established" in both official languages when the two versions are signed by the authorized regulatory authority before being printed and published. In short, it would not be constitutional to adopt a law in just one of the official languages. Barring exceptions, laws are generally written simultaneously in both official languages.