Hello Santiago,
Regarding Hawker book that you mentioned, take a look at
http://forum.12oclockhigh.net/showthread.php?t=55717
The second one with the Messerschmitt at cover page is "Ratni dnevnik" - Combat Diary of 1 & 2. Aviation Brigade VVKJ in 1941 April War. The book is in Serbian language.
Cheers
Aleks