'E149: Sorry, no help for LanguageTool' on NVIM v0.4.3 and LanguageTool-5.1

[ttxtea]

Following the installation instructions with

let g:languagetool_jar='$HOME/languagetool/languagetool-standalone/target/LanguageTool-5.1-SNAPSHOT/LanguageTool-5.1-SNAPSHOT/languagetool-commandline.jar'

in the .vimrc.

and

.vim/doc/LanguageTool.txt
.vim/plugin/LanguageTool.vim

in place.

running vim -c 'helptags ~/.vim/doc' did not give any verbose output.

There is not realy any error except E492: Not an editor command: LanguageToolCheck