C# or SQL function required for amount to words in thai

ALTER FUNCTION [dbo].[fnNumberToThaiWords](@Number as BIGINT)

    RETURNS NVARCHAR(1024)

AS

BEGIN

      DECLARE @Below20 TABLE (ID int identity(0,1), Word NVARCHAR(32))

      DECLARE @Below100 TABLE (ID int identity(2,1), Word NVARCHAR(32))

      INSERT @Below20 (Word) VALUES
                        ( N'ศูนย์'), (N'หนึ่ง'),(N'สอง' ), (N'สาม'),
                        ( N'สี่' ), ( N'ห้า' ), ( N'หก' ), ( N'เจ็ด' ),
                        ( N'แปด'), ( N'เก้า'), ( N'สิบ'), ( N'สิบเอ็ด' ),
                        ( N'สิบสอง' ), ( N'สิบสาม' ), ( N'สิบสี่'),
                        ( N'สิบห้า' ), (N'สิบหก' ), ( N'สิบเจ็ด'),
                        (N'สิบแปด' ), ( N'สิบเก้า' )
      
	   INSERT @Below100 VALUES (N'ยี่สิบ'), (N'สามสิบ'),(N'สี่สิบ'), (N'ห้าสิบ'),
                               (N'หกสิบ'), (N'เจ็ดสิบ'), (N'แปดสิบ'), (N'เก้าสิบ')

DECLARE @English Nvarchar(1024) =
(
  SELECT Case

    WHEN @Number = 0 THEN  ''

    WHEN @Number BETWEEN 1 AND 19
      THEN (SELECT Word FROM @Below20 WHERE ID=@Number)

   WHEN @Number BETWEEN 20 AND 99  
     THEN  (SELECT Word FROM @Below100 WHERE ID=@Number/10) + dbo.fnNumberToThaiWords( @Number % 10)

   WHEN @Number BETWEEN 100 AND 999  
     THEN  (dbo.fnNumberToThaiWords( @Number / 100))+N'ร้อย' + dbo.fnNumberToThaiWords( @Number % 100)

   WHEN @Number BETWEEN 1000 AND 999999
     THEN  (dbo.fnNumberToThaiWords( @Number / 1000))+N'พัน' + dbo.fnNumberToThaiWords( @Number % 1000) 

   WHEN @Number BETWEEN 1000000 AND 999999999  
     THEN  (dbo.fnNumberToThaiWords( @Number / 1000000))+N'ล้าน' + dbo.fnNumberToThaiWords( @Number % 1000000)

   WHEN @Number BETWEEN 1000000000 AND 999999999999  
     THEN  (dbo.fnNumberToThaiWords( @Number / 1000000000))+N'พันล้าน'+ dbo.fnNumberToThaiWords( @Number % 1000000000)

   WHEN @Number BETWEEN 1000000000000 AND 999999999999999  
     THEN  (dbo.fnNumberToThaiWords( @Number / 1000000000000))+N'ล้านล้าน'+ dbo.fnNumberToThaiWords( @Number % 1000000000000)

  --WHEN @Number BETWEEN 1000000000000000 AND 999999999999999999  

  --   THEN  (dbo.fnNumberToThaiWords( @Number / 1000000000000000))+' Quadrillion '+

  --       dbo.fnNumberToThaiWords( @Number % 1000000000000000)

  --WHEN @Number BETWEEN 1000000000000000000 AND 999999999999999999999  

  --   THEN  (dbo.fnNumberToThaiWords( @Number / 1000000000000000000))+' Quintillion '+

  --       dbo.fnNumberToThaiWords( @Number % 1000000000000000000)

        ELSE N'ข้อมูลที่ไม่ถูกต้อง' END

)



SELECT @English = RTRIM(@English)
SELECT @English = RTRIM(LEFT(@English,len(@English)-1))
                 WHERE RIGHT(@English,1)='-'
RETURN (@English)

END