Related Rule
Germany
Practice Relating to Rule 125. Correspondence of Persons Deprived of Their Liberty
Germany’s Military Manual (1992) states: “Not more than one week after the arrival at a camp, every prisoner of war shall be enabled to inform his family and the Central Prisoners of War Agency by letter of his captivity and to regularly correspond with his relatives henceforth.” 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 721.
Germany’s Soldiers’ Manual (2006) states:
Immediately upon their capture, or not more than one week after their arrival at a camp, prisoners of war shall be enabled to inform, in writing, their families and the Central Prisoners of War Information Agency at the International Committee of the Red Cross (19, avenue de la Paix, CH-1202 Geneva) of their capture. 
Germany, Druckschrift Einsatz Nr. 03, Humanitäres Völkerrecht in bewaffneten Konflikten –Grundsätze, Erarbeitet nach ZDv 15/2, Humanitäres Völkerrecht in bewaffneten Konflikten – Handbuch, DSK SF009320187, Bundesministerium der Verteidigung, R II 3, August 2006, p. 7.