Currently texi support such output format:

   Info Plain HTML DVI PDF XML Docbook

Originally texi support 7-bit input text which without no cost
extended to 8-bit Latin encoding.

With  '--enable-encoding' and '@documentlanguage' and
'@documentencoding' it is possible set custom encoding
ever UTF-8.

And with:

   @documentencoding UTF-8

I can produce correct XML, DOCBOOK, HTML and with some issue plain text.

But not DVI PDF like previously written:

   http://thread.gmane.org/gmane.comp.tex.texinfo.general/1019

because of lack of UTF-8 support by Plain TeX.

Is there any case to make good pdf output?

I think that DocBook can be used for this purpose. Is there any
specific XSL for producing same style pdf as by '\input texinfo'?

It is usual create pdf from texi using DocBook?