Force set enc/fenc/tenc same as your environment variable.

gistfile1.vim

    " Multi-encoding Setting
    " Auto detect Asia language environment. your vim should be compiled with multi_byte option
    if has("multi_byte")
        "set bomb
        set fileencodings=ucs-bom,utf-8,cp936,big5,euc-jp,euc-kr,latin1
        " CJK environment detection and corresponding setting
        if v:lang =~ "^zh_CN"
            " Use cp936 to support GBK, euc-cn == gb2312
            set encoding=cp936
            set termencoding=cp936
            set fileencoding=cp936
        elseif v:lang =~ "^zh_TW"
            " cp950, big5 or euc-tw
            " Are they equal to each other?
            set encoding=big5
            set termencoding=big5
            set fileencoding=big5
        elseif v:lang =~ "^ko"
            " Copied from someone's dotfile, untested
            set encoding=euc-kr
            set termencoding=euc-kr
            set fileencoding=euc-kr
        elseif v:lang =~ "^ja_JP"
            " Copied from someone's dotfile, untested
            set encoding=euc-jp
            set termencoding=euc-jp
            set fileencoding=euc-jp
        endif
        " Detect UTF-8 locale, and replace CJK setting if needed
        if v:lang =~ "utf8$" || v:lang =~ "UTF-8$"
            set encoding=utf-8
            set termencoding=utf-8
            set fileencoding=utf-8
        endif
    endif