Problem related to the charset converter for gvim on windows,
From help :usr_45
, it says:
Using different languages only works when Vim was compiled to handle it. To find out if it works, use the ":version" command and check the output for "+gettext" and "+multi_lang". If they are there, you are OK. If you see "-gettext" or "-multi_lang" you will have to find another Vim.
If there is "-gettext" or "-multi_lange", or "-iconv", you need to download proper library your own for windows, see this post https://superuser.com/questions/207264/gvim-utf-8-in-windows for more information and downlinks for the library on windows