Sometimes they can look like this:
That’s the telegram sent by Count Berchtold, the Austro-Hungarian Foreign Minister, to the government of Serbia on 28 July 1914. It was written in French, the standard language of diplomacy in those days. The telegram was sent from Vienna to the Austro-Hungarian ambassador in Belgrade, who then passed it on to Prime Minister Pašić in person. This was the usual procedure for war declarations in the 20th century.
The text reads:
Le Gouvernement royal de Serbie n’ayant pas repondu d’une manière satisfaisante à la note qui lui avait été remise par le Ministre d ‘Autriche-Hongrie à Belgrade à la date du 23 juillet 1914, le gouvernement impérial et royal se trouve dans la nécessité de pourvoir lui-même à la sauvegarde de ses droits et intérêts et de recourir à la force des armes . Par conséquent L’Autriche-Hongrie se considère désormais en état de guerre avec la Serbie.
Le ministre des Affaires étrangères d’Autriche-Hongrie
Comte Berchtold
The Royal Government of Serbia having not responded in a satisfactory manner to the note which had been given to it by the Minister of Austria-Hungary at Belgrade on the date of 23 July 1914, the Imperial and Royal Government finds itself under the necessity of providing by itself for the safeguarding of its rights and interests and of resorting to force of arms. In consequence Austria-Hungary considers itself henceforth in a state of war with Serbia.
The Minister of Foreign Affairs of Austria-Hungary
Count Berchtold