How to change default language on doc

Hi,
I’m looking to change default language on freshly created docx and pptx.
On my docker test setup, I found this directory : /opt/seafile/seafile-server-latest/seahub/media/office-template/
I try to mount a custom directory with docker’s volume, but after restat seafile only show a blank page and no errors in logfiles.
Any suggestions ?

Fixed,
volume needs to be mounted on /opt/seafile/seafile-version/seahub/media/office-template.