Languages have varying costs of entry and mastery. The relative cost depends on what languages one already knows. But some language features are rarer and more

Languages have varying costs of entry and mastery. The relative cost depends on what languages one already knows. But some language features are rarer and more difficult (declensions, conjugations, symbols, tones, etc). The size of the active vocabulary matters a great deal. But the availability of the language matters perhaps most of all.