All data in splunk indexes is stored as UTF8.
However, for the log contents, you can specify the encoding to convert from, using CHARSET in props.conf.
On the third hand, though, for filenames, there is no such functionality. On UNIX we assume filenames are UTF8 and on windows we assume they are UTF16. On Windows this is pretty much always true, but on UNIX you can choose to present filenames in other encodings.
For your own sanity I strongly recommend you only use UTF8 filenames on modern Unix systems. However, if your use-case and goals require you to do otherwise, please tell us about this in a support ticket. This is a known limitation and there is an entry in the work database relating to this limitation, but understanding why it matters will help prioritize.
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