I don't understand why subjects such as Latin/French etc scale up by so much whereas Arabic,bosnian etc don't . 
My understanding is that Latin goes up so much because largely only really academically strong schools offer it.
The scaling is a reflection of the scores that the people in a subject (the cohort, to use a Latin word..) achieve for their other subjects.
Additionally, for languages, there is an automatic +4 scaling, because the government wants to increase communication/interaction with other countries. Such an explanation seems a bit weird given Latin's simply enormous prominence throughout the world. Nonetheless...
But so the difference between say Latin and Bosnian is that the schools that offer those two subjects, and hence the academic quality of those two cohorts is quite different. The variance in the scaling suggests that the Latin cohort of students generally outperform the Bosnian cohort in the other subjects undertaken by those students.
But why is it that more academically talented students take French or German and not Bosnian or Albanian? - that's a tough question to answer.
Perhaps because the most academically strong schools don't offer the latter two, and hence the best academic kids don't get a chance to study them? I'm really not sure.