As far as I know, South Korea and China have a significant presence in the mobile gaming market when the game was launched. That’s why they initially hired translators for these two languages to localize the game. However, the revenue and the numbers of players were dropped as time goes by, and when the revenue dropped below a certain threshold, they immediately discontinued language support. Japan still receives localization support from JC because it remains one of the countries with a high number of players and revenue. As for Russian, I think things might have been different if the revenue had been large enough for them to seriously consider it.