Since version 3.7, I guess Alfred stopped localizing date snippets.
My system is in French.
I have created a snippet, with the keyword ldate : {date:yyyy/MM/dd'} {date:EEEE}
In earlier versions of Alfred, it used to return 2018/11/14 Mercredi, with date:EEEE using the current UI language.
Since version 3.7, it returns 2018/11/14 Wednesday. The language is no longer taken into account.