What ever is the language setting of TiddlyWiki (with TiddlyDesktop), the days and months are ALWAYS in French!
This happened with a call like this:
<$edit-text tiddler="$:/temp/presta/date" tag=“input” type=date />
I think the browser language is used instead of the TW language setting (I have not installed any pluging before making some tests on a fresh TW).
When I use Firefox alone (Windows 10) with language (in browser setting) set to English the days and months are in English. Switching back to French: the days and months are in french.
Same behaviour with my tablet (using Android 8.1.0, Tidloid 2.4.2, browser Brave 1.50.121 Chromium 112.0.5615.138), but every thing is alright if I open TW directly in a browser.