The question of course is, how can I make both Linux and Solaris behave equal?

Um, fix your locales (the actual system files ... man locale..) so they match? See https://help.ubuntu.com/community/Locale and perllocale

FWIW, on my win32 I get the same as your solaris

0:      Sort_1Test
1:      Sort_Test
2:      Sort1_Test
3:      SortTest
4:      Test_1Sort
5:      Test_Sort
6:      Test1_Sort
7:      TestSort
[download]

Which probably means I don't have that locale installed and/or the locale use locale; uses isn't the same as what you want it to be .... perllocale might have something to say on how to check what locales are available and which one is being used