Asking for the zero'th index is special - it returns a string descriptor that contains all the language IDs supported by the device. Typically there aren't many - often only one. The language IDs are 16 bit numbers, and they start at the third byte in the descriptor. See USB 2.0 specification, section 9.6.7, for more information on this.

public bool GetLangIDs(
	out short[] langIDs
)

Public Function GetLangIDs ( _
	<OutAttribute> ByRef langIDs As Short() _
) As Boolean

public:
virtual bool GetLangIDs(
	[OutAttribute] array<short>^% langIDs
) sealed