20.1.5 Isearch for Non-ASCII Characters

To enter non-ASCII characters in an incremental search, you must use an input method (see Input Methods). If an input method is enabled in the current buffer when you start the search, you can use it while you type the search string also. Emacs indicates that by including the input method mnemonic in its prompt, like this:

     I-search [im]:

where im is the mnemonic of the active input method. You can toggle (enable or disable) the input method while you type the search string with C-\ (isearch-toggle-input-method). You can turn on a certain (non-default) input method with C-^ (isearch-toggle-specified-input-method), which prompts for the name of the input method. The input method you enable during incremental search remains enabled in the current buffer afterwards.