The only thing I can think of that might work without rewrite rules is using the home page settings:
Settings > Content -> Default alias path
Set this value to "/en" (type don't select)
Settings > URLs and SEO -> Default page
Set this drop down to "Use page defined by default alias path"
Keep in mind this does a permanent 301 redirect.
See more info in the docs at
docs.xperience.io/k12sp/.../settings-urls-and-seo