How do I convert this MSSQL stored procedure to a mysql stored procedure?

USE [tt]
GO
/****** Object: StoredProcedure [dbo].[_getNewsPagedSorted] Script Date: 6-11-2013 15:09:22 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

-- =============================================
-- Author: <Author,,Name>
-- Create date: <Create Date,,>
-- Description: <Description,,>
-- =============================================
ALTER PROCEDURE [dbo].[_getNewsPagedSorted]
@startRowIndex int
,@maximumRows int
,@sortExpression nvarchar(20)
,@lang nvarchar(20)

AS
BEGIN
SET NOCOUNT ON;

if @sortExpression=''
set @sortExpression='publishdate DESC'

declare @SQL nvarchar(max)

set @SQL='SELECT * FROM (select ROW_NUMBER() OVER (ORDER BY '+@sortExpression+') as RowNum,
* FROM news WHERE publishdate <=getdate() and lang=''' + @lang + ''') as info
WHERE RowNum > '+STR(@startRowIndex)+' AND RowNum <= ('+STR(@startRowIndex + @maximumRows)+') '

EXEC sp_executesql @SQL



END