. Q stands for QUESTION (in French)
The first 3 letters Q codes ( 1904 ) were the first aim at standardising communication in W/T (morse) and replaced the Merchant Navy 2 letters codes .They were all questions and all started with : What is.... ?
After the treaty of Versailles in 1918, a more complex form (additional Q codes ) were developped to cater more specifically for International aviation. The original text (like everything else in those days relating to communications ) were in French. they remained so until 1944, where PICAO and the Chicago convention established English as the commincation method and developped International R/T procedures.
Q codes in W/T were used until late 1950's especially in remote areas.The British Comet Jet was equipped with a W/T operator seat in the cockpit. the last W/T ground ATC station was Recife covering the South Atlantic and closed down in late 1960's.
The good thing about Q codes is that they eliminated the need to speak a common language when overflying or landing in other countries.The military kept them much longer than the civilians.