On the paper are they covered, but currently there are no trains between Turkey and Sofia (Bulgaria) and between Bulgaria-Serbia-Croatia. You could go via Romania to Budapest (Hungary) and from there to Ljubljana. 

As said above

Journeys are covered but From Turkey via Sofia - Belgrade - Zagreb currently no Service :/ 

From Sofia via Vidin/Craiova - Budapest - Lubljana/Zagreb or Sofia- Ruse- Bucharest- Budapest/Vienna - Lubljana/Zagreb 

Between Budapest and Lubljana up to 4trains per day 2daytrains via Graz/Maribor 

1daytrain via Hodos 

1Nighttrain in Summer :) 

For the last 3 you have to cough up fairly expensive (IF those HiSpeedo chosen, and certainly for INTernational) supplements+REServations. These can be made lower by changing more and using local trains=takes (much) longer.

IF you watch the money in your account-and IF youre a bit flexible and wiling to take buses (these cover the sectors explained above as out of trains), its likely cheaper-and also easier to book individual advance tickets (these tie you in into those days/trains).

Also check seat61, aimed at overland travelling Brits to/fro that island in the NorthSea-it has good overviews about how to.