Did you resolve the issue at all? I have same problem - effectively some of our users have multiple languages in their Chrome Browser:

With it set like this it ignores all the language protections I've put in place in the app - including a variable which detects the browser language on app startup and if it's not en-GB then it sets their language to be US English. I've even got additional settings for the form date picker fields.
Despite this users with Chrome and multiple languages don't just get the date pulled from SharePoint in a different format...but it's actually giving completely random future dates that don't corollate to the shared date, nor even the current date. This is far from ideal because whilst on a case by case basis I can ask people to use workarounds like a different browser or kindly removing languages and resetting chrome, clearly I can't make that commonly understood across a large organisation - and where review dates are being set in the app, it's doing to be overriding with nonsense dates when people submit a form.
Here's what I have in my App OnStart property:
If(Language() = "en-GB", Set(varLangFormat, "[$-en-GB]dd/mm/yyyy"), Set(varLangFormat,"[$-en-US]mm/dd/yyyy"));
In DatePicker dropdowns in galleries I have Language also set to:
If(Language() = "en-GB", "en-GB", "en-US")
And in the properties of a Form's date picker DefaultDate for example:
If(
MyForm.Mode=FormMode.Edit,
Text(Today(),varLangFormat),
Text(Parent.Default,varLangFormat)
)
The problem has been flagged to me specifically in the Form that's using the above DefaultDate syntax....
Appreciate if anyone has advice how to overcome this. Thanks!