In the first place, the price of the translation is a matter of supply and demand: the rarer the language and the fewer translators working in that language, the higher the price will be. Rarity is a relative concept, of course; a Dutch translator living in Uzbekistan will be much more of a rarity than a Dutch translator in the Netherlands and will therefore be able to charge a higher rate.
Moreover, some languages, such as Asian languages, are simply more labour-intensive than others. For instance, producing a text in Japanese, a language with more than 8,000 characters, is considerably more time-consuming than producing a text in English. Furthermore, the structure of a text written in a Western language will need to be adapted to Japanese cultural norms as well. The differences involved can be extremely subtle and difficult to grasp, which makes translating into Japanese a highly complex undertaking and entails additional expense.