Modify Maintenance plugin page

Hi
I'm fairly new to GRAV and love it but I must be missing something here:
In maintenance mode I want to include addtional text in place of " Please check back soon.." but can't find out whhere the text originates from.
I checked 'maintenance.md' and 'maintenance.html.twig' and would appreciate it if anybody can shed soem light on this.
Thanks

@jerry, Since the message will probably be multi-lingual, try 'user/plugins/maintenance/languages.yaml'

@pamtbaau, Thanks. I knew it had to be obvious.
Still trying to get my head around the structure and making minor mods to see if the result is as expected. I want to embed some specific text into the site offline message