We have mp3 file with ID3 v.1 in UTF8 and ID3 v2.4 in UTF8. All ID3 info in Cyrillic, encoded in UTF8.
ID3v1 does not support Unicode so that part is not possible.
The rest sounds fine.
As far as I understood Centova uses UFT8 encoding for all web pages.
Yes, Centova Cast uses UTF8 for everything internally.
In settings for this channel we have Character Encoding set to CP1251: Cyrillic (it could be set to ISO-8859-5: Latin/Cyrillic too).
This is irrelevant if you have Unicode ID3v2 tags in your MP3s. The ID3v2 spec provides for two character encodings -- "Unicode" or "not Unicode". Obviously that's a bit silly because if you're using "not Unicode" then you have no way of knowing what encoding you ARE using, which is why the "Character encoding" setting exists.
But if you have properly encoded the MP3s with Unicode ID3v2 tags, then they will be marked as such in the ID3v2 tag headers. In that case, Centova Cast will completely ignore the character encoding setting and will process the tags directly as Unicode (choosing UTF8, UTF16, etc. appropriately depending on the BOM).
If I am right, the system works this way: ID3 info in UTF8 converts to CP1251.
No. Per above, if it's UTF8 (or otherwise Unicode) encoded it is used as-is.
Shoutcast DNAS Status page shows information in UFT8 by default.
That depends on which SHOUTcast DNAS version you're talking about. If you mean DNAS1, then no... it has no concept of character encoding and just dumps the raw strings in its output. That leads to all kinds of character encoding problems.
DNAS2 uses UTF8 output by default, though.
In this case we see unreadable info in Cyrillic (see CP1251_page_encoding screenshot).
It's hard to follow your example without seeing any context -- where are those screenshots from? DNAS? Or a Centova Cast widget? If they're from DNAS, that's a black background which implies DNAS1, in which case it's not unexpected to see character encoding problems due to DNAS1's lack of proper character encoding support.
Now question. Is it possible to add one extra point for Character Encoding in Settings like UFT8 or DO NOT CONVERT?
No, that's the default behavior already so it's unnecessary to add a separate option for it.