Do you have any tools that teach you how to use functions in the Vim plug-in or Linux tool?

If you really want to translate it into Japanese, you'll need the Japanese document first, and then you'll need to work with the tools to browse it
The quickest way to do this is to use Web data such as Python 3.7.3 document
For example, if you want to use a web browser w3m that can be used in a terminal, change the function written by the previous queueu1829 and do the following

 function!s:pyhelp(word)abort
    execute'terminal++ close w3m-o confirm_qq=0 https://docs.python.org/ja/3/library/functions.html\\#'.a:word
endfunction
command!-nargs=1PyHelp call<SID>pyhelp(<f-args>)
setlocal keywordprg= —PyHelp

Execute can be used as well as other browsers, or Firefox can be used if you have never used a CLI browser before.

Answer on the assumption that the vim configuration is under through /.vim.

Create c.vim and python.vim in ~/vim/ftplugin and add Shift+k.
If I remember correctly, by default, c++ will read c.vim, but if it doesn't work, please add .vim.

$catc.vim

let$MANPAGER="vim-M+MANPAGER-" 
if has('terminal')
    let&l:keywordprg=':terminal++close++norestore man3'
    " or
    "let&l:keywordprg=":vertical terminal++close++norestore man3"
else
    let&l:keywordprg='man3'
endif

$cat python.vim

"Uncomment for your needs.
US>"let$LESS=substate($LESS, '--quit-if-one-screen\>', '', 'g')
if has('terminal')
    let&l:keywordprg=':terminal++close++norestore pydoc3
    " or
    "let&l:keywordprg=":vertical terminal++close++norestore pydoc3"
else
    let&l:keywordprg='pydoc3'
endif

For more information, try :help keywordprg in vim.

If you want to translate man into Japanese, you can install manpages-ja and manpages-ja-dev for Debian/Ubuntu descent.

 sudo apt install manpages-ja manpages-ja-dev

Unfortunately, pydoc3 cannot be translated into Japanese.For more information, see Can I translate pydoc/pydoc3 into Japanese?