I did a test creating a file with the accented letters (my language is LANG=it_it), getting these results:
$ date > prova-accentate-àèéìòù-test
$ ls -ll
-rw-r--r-- 1 root root 31 9 set
21.34 prova-accentate-àèéìòù-test
$ ls prova-accentate-àèéìòù-test | hd
00000000 70 72 6f 76 61 2d 61 63 63 65 6e
74 61 74 65 2d |prova-accentate-|
00000010 e0 e8 e9 ec f2 f9 2d 74 65 73 74 0a
|àèéìòù-test.|
This test is ok
---
$ kate prova-accentate-àèéìòù-test
$ ls -ll
-rw-r--r-- 1 root root 31 9 set 21.35
prova-accentate-ￜￜￜￜￜￜ-test
$ ls prova-accentate-ￜￜￜￜￜￜ-test | hd
00000000 70 72 6f 76 61 2d 61 63 63 65 6e
74 61 74 65 2d |prova-accentate-|
00000010 ef bf bd ef bf bd ef bf bd ef bf bd ef bf bd ef
|ￜￜￜￜￜï|
00000020 bf bd 2d 74 65 73 74 0a
|¿œ-test.|
This test has an unexpected result,
It seems that Kate does not manage these characters...