Hi,
Thanks for using our plugins and I can help you out here.
You are talking about the datepicker in the Community Calendar where users can add events correct?
It is correct that one is set by javascript.
Unfortunately, changing the javascript is the only option for this as php snippets cannot cannot change it.
This post gives almost as much information as we can provide on making that change, which I think you already has looked at:
https://theeventscalendar.com/support/forums/topic/cant-change-date-format-by-community-preferences/
If you would like to request that feature please head to our UserVoice Page and add your own or upvote that feature as they will increase the chances of it being added to a future version.
http://tribe.uservoice.com/forums/195723-feature-ideas
I can help answer some more questions, let me know.
Thanks