Please also provide a function and command to set this. E.g. C-x4m for langtool-mother-tongue and provide function and command for setting language, e.g. C-x4l for langtool-language

Defaults for both are empty and will imply English. For both functions, allow listing of all options. These can be obtained via:
ls /usr/local/share/languagetool/rules/|grep ^..$
or
find /usr/local/share/languagetool/rules/* -type d

from emacs-langtool.

Thanks for your request.

Please provide a setting for .emacs for mothertongue.

I implement -m option by creating new customize variable langtool-mother-tongue.
Please put like following to your .emacs

(setq langtool-mother-tongue "en")

Please also provide a function and command to set this. E.g. C-x4m for langtool-mother-tongue and provide function and command for setting language, e.g. C-x4l for langtool-language

I think mother tongue will not be so often changed.
So this command and function is not provided.

You can change the language to change the setting of langtool-default-language
Or call langtool-check-buffer with a prefix arg (probably C-u) read language to apply only current session.

This issue is first time that I have received on github. If there is any problem, please do not hesitate to ask.

from emacs-langtool.

Thanks for your answer. Mother tongue indeed doesn't need changing a lot. ;)

Could you implement at least implement function for langtool-set-language which will also provide all available languages?

from emacs-langtool.

I have done. M-x langtool-switch-default-language

from emacs-langtool.