If I paste a string from some web page into an Emacs buffer sometimes it will show the Unicode representation of some characters with a backslash and some octal code. How can I convert this to the character representation?
Specify whether you are using Emacs in a terminal or GUI Emacs.
Use a font in Emacs that can display that Unicode character.
If your buffer is Unibyte (single-byte), then consider using multibyte instead. In any case, see the Emacs manual, node Unibyte Mode and the Elisp manual, node Text Representations. Consider using function
set-buffer-multibyte to convert the buffer to multibyte. See also (elisp) Disabling Multibyte (not to disable it, but for more info about it).
Copying the whole buffer and pasting it into another new buffer somethimes helps here.