The Croatian translation is also called Gospodar Prstenova and the only way to tell the difference without looking inside at the text is to note where the books are published. If they are published in Serbia or Montenegro, they are Serbian. If they are published in Croatia, they are Croatian. One other difference is that in Croatian Silmarillion is spelled as in English, but in Serbian it is spelled Silmarilion.
Gospodar Prstenova (Serbian C), purchased on-line from docrocks82 on ebay in 2020 (paperback)
Tolkien, J. R. R., Gospodar Prstenova, trans. by Zoran Stanojević (Esotheria, 1995), 1, Družina Prstena. ISBN: 86-81585-69-X
——, Gospodar Prstenova, trans. by Zoran Stanojević (Esotheria, 1995), 2, Dve Kule. ISBN: 86-81585-70-3
——, Gospodar Prstenova, trans. by Zoran Stanojević (Esotheria, 1995), 3, Povratak Kralja. ISBN: 86-81585-71-1
While the art on the front covers portrays events from the correct volumes that it appears on, the back covers for TT and RK illustrate events from FR and TT respectively--the battle with the Balrog on TT and climbing the stairs of Cirith Ungol on RK.
Gospodar Prstenova (Serbian B), purchased on-line from Kristina Gubić, Buzet, Croatia on Njuškalo in 2019 (hardback)
Tolkien, J. R. R., Gospodar Prstenova, trans. by Zoran Stanojević (Esotheria, 2002), 1, Družina Prstena. ISBN: 86-7348-067-1
——, Gospodar Prstenova, trans. by Zoran Stanojević (Esotheria, 2002), 2, Dve Kule. ISBN: 86-7348-068-X
——, Gospodar Prstenova, trans. by Zoran Stanojević (Esotheria, 2002), 3, Povratak Kralja. ISBN: 86-7348-069-8
Zinaida Biro put me in contact with Kristina Gubić on Njuškalo in order to purchase this edition.
While the art on the back cover correctly matches an event within FR, the events portrayed on the back covers of TT and RK do not. The back of TT shows the visit of Gimli and Legolas to the Glittering Caves which happens in RK although Gimli describes the caves to Legolas in TT. The back of RK shows Frodo, Sam, and Gollum climbing the stairs of Cirith Ungol from TT.
This edition is the Serbian translation published in Montenegro. This version is sometimes known as the "Montenegrin" translation although Serbian and Montenegrin are virtually identical and this edition is the Serbian translation by the Serbian translator.
Gospodar Prstenova (Serbian A), purchased on-line from Terazjie, Belgrade, Serbia on Amazon in 2016 (hardback)
Tolkien, J. R. R., Gospodar Prstenova, trans. by Zoran Stanojević (Narodna knjiga, 2007), 1, Družina Prstena. ISBN: 978-86-84237-56-1
——, Gospodar Prstenova, trans. by Zoran Stanojević (Narodna knjiga, 2007), 2, Dvije Kule. ISBN: 978-86-84237-60-8
——, Gospodar Prstenova, trans. by Zoran Stanojević (Narodna knjiga, 2007), 3, Povratak Kralja. ISBN: 978-86-84237-62-2
Gospodar Prstenova (Serbian E), purchased on-line from Terazije on Amazon in 2022 (hardback in box [box design below])
Tolkien, J. R. R., Gospodar Prstenova, trans. by Zoran Stanojević (Publik Praktikum, 2018), 1, Družina Prstena. ISBN: 978-86-6035-586-9
——, Gospodar Prstenova, trans. by Zoran Stanojević (Publik Praktikum, 2018), 2, Dve Kule. ISBN: 978-86-6035-587-6
——, Gospodar Prstenova, trans. by Zoran Stanojević (Publik Praktikum, 2018), 3, Povratak Kralja. ISBN: 978-86-6035-588-3
Hobit (Serbian [H] B), purchased on-line from Terazije on Amazon in 2022 (hardback)
Tolkien, J. R. R., Hobit, trans. by Danko Ješić (Publik Praktikum, 2022). ISBN: 978-86-6035-825-9
Gospodar Prstenova (Serbian D), purchased on-line from Knjiga.ba, Tuzla, Bosnia & Hercegovina in 2022 (paperback)
Tolkien, J. R. R., Gospodar Prstenova, trans. by Zoran Stanojević (Nova Knjiga, 2019), 1, Družina Prstena. ISBN: 978-86-7470-834-7
——, Gospodar Prstenova, trans. by Zoran Stanojević (Nova Knjiga, 2019), 2, Dvije Kule. ISBN: 978-86-7470-835-4
——, Gospodar Prstenova, trans. by Zoran Stanojević (Nova Knjiga, 2019), 3, Povratak Kralja. ISBN: 978-86-7470-837-8
Hobit (Serbian [H] A), purchased on-line from Knjiga.ba, Tuzla, Bosnia & Hercegovina in 2022 (paperback)
Tolkien, J. R. R., Hobit, ili Tamo i Natrag, trans. by Danko Ješić (Nova Knjiga, 2019). ISBN: 978-86-7470-855-2
Silmarilion (Serbian [S]), purchased on-line from Knjiga.ba, Tuzla, Bosnia & Hercegovina in 2022 (paperback)
Tolkien, J.R.R. Silmarilion. Edited by Christopher Tolkien. Translated by Vesna Stojković. Nova Knjiga, 2019