It sounds like the server isn’t properly configured for the non-www URL. I suggest you add a Page Rule to redirect:
Match: example.com/*
Setting: Forwarding URL (301) to https://www.example.com/$1
You can leave the $1 off if you don’t want to forward the path from the non-url redirect.
I didn’t notice this problem before Cloudflare activation from my siteGround hosting plan. Cloudflare needed domains with www and made me change something in dns.
So I think that the problem AND the solution should come from Cloudflare…
You can troubleshoot this by setting the non-www record to DNS Only. Give it five minutes to take effect, then see if it still points to English version.
You might have to ask Siteground about this. I don’t know what their Cloudflare setup looks like. On Cloudflare accounts, it’s in the DNS Records list.
I have no idea why your site does not work as expected. Siteground is your best source of information, as they’re your host and control your entire configuration.