How to sort list of String without considering Special characters and with case insensitive

[san]

Please let me know how to sort the list of String in either ascending / descending order without considering special characters and case.
ex: list1=['test1_two','testOne','testTwo','test_one']
Applying the list.sort /sorted method results in sorted list ['test1_two', 'testOne', 'testTwo', 'test_one']
but the without considering the special characters and case it should be 
['testOne','test_one', 'test1_two','testTwo'] OR ['test_one','testOne','testTwo', 'test1_two' ]

list.sort /sorted method sorts based on the ascii value of the characters but Please let me knwo how do i achieve my expected one