Cannot build helptags

[NihilityT]

Problems summary

I tried to add a plugin chemzqm/wxapp.vim and run call dein#recache_runtimepath(), but I got an error:

E670: Mix of help file encodings within a language: /home/.../.dein/doc/wxapp.txt

Expected

make the helptags can to build tags for wxapp.vim

Environment Information (Required!)

• dein.vim version(SHA1): c2416cf

• OS: Ubuntu 18.04.2 LTS

• Vim/neovim version: Vim 8.1

Provide a minimal .vimrc with less than 50 lines (Required!)

" normal

set nocompatible
let $bundle = expand('~/.vim/bundle')
let $dein_dir = expand($bundle.'/repos/github.com/Shougo/dein.vim')
set runtimepath^=$dein_dir

call dein#begin($bundle)

call dein#add('chemzqm/wxapp.vim')

call dein#end()

" error

set nocompatible
let $bundle = expand('~/.vim/bundle')
let $dein_dir = expand($bundle.'/repos/github.com/Shougo/dein.vim')
set runtimepath^=$dein_dir

call dein#begin($bundle)

call dein#add($dein_dir)
call dein#add('chemzqm/wxapp.vim')

call dein#end()

The reproduce ways from Vim starting (Required!)

1. use the first vimrc and run call dein#recache_runtimepath(), the helptags can build tags and work well.
2. add call dein#add($dein_dir) to vimrc and run call dein#recache_runtimepath(), will get an error E670

Upload the log messages by :redir and :message (if errored)

[dein] Error generating helptags:
[dein] Vim(helptags):E670: Mix of help file encodings within a language: /home/.../.dein/doc/wxapp.txt
[dein] function dein#recache_runtimepath[1]..dein#install#_recache_runtimepath[1
9]..<SNR>20_helptags, line 12

[Shougo]

Sorry. It is wxapp's documentation problem.

https://github.com/chemzqm/wxapp.vim/blob/master/doc/wxapp.txt
It includes Chinese characters for English documentation.

[Shougo]

Same problem exists when you copy wxapp's documentation in ~/.vim/doc.
So it is not dein's problem.