Related Rule
Canada
Practice Relating to Rule 99. Deprivation of Liberty
Section C. Prompt information on the reasons for deprivation of liberty
Canada’s LOAC Manual (1999) provides: “Any person arrested, detained or interned for actions related to the armed conflict shall be informed promptly, in a language that person understands, of the reasons why these measures have been taken.” 
Canada, The Law of Armed Conflict at the Operational and Tactical Level, Office of the Judge Advocate General, 1999, p. 11-8, § 64.
Canada’s LOAC Manual (2001), in its chapter on the treatment of civilians in the hands of a party to the conflict or an occupying power and, more specifically, in a section entitled “Additional Protocol I”, states:
Any person arrested, detained or interned for actions related to the armed conflict shall be informed promptly, in a language that person understands of the reasons why these measures have been taken. 
Canada, The Law of Armed Conflict at the Operational and Tactical Levels, Office of the Judge Advocate General, 13 August 2001, § 1135.3.
In the Charkaoui case before the Supreme Court of Canada in 2007, in which the three appellants challenged the constitutionality of the provisions of Canada’s Immigration and Refugee Protection Act (IRPA) under which they had been detained for suspected links to terrorist activities, the Supreme Court held:
28. The overarching principle of fundamental justice that applies here is this: before the state can detain people for significant periods of time, it must accord them a fair judicial process …
29. This basic principle has a number of facets [including] … the right to know the case put against one, and the right to answer that case
53… [A] fair hearing requires that the affected person be informed of the case against him or her, and be permitted to respond to that case. 
Canada, Supreme Court, Charkaoui case, Judgment, 23 February 2007, §§ 28, 29 and 53.
[emphasis in original]