Pinterest documentation links redirect to 404, when language is set to Simplified Chinese

[tomalec]

This issue was found at https://github.com/woocommerce/pinterest-for-woocommerce/pull/261#discussion_r750081852

Describe the bug:

Documentation links without a specified language, redirect to /zh/…, then redirect to zh/zh/…, and so on, which eventually ends on 404 Error.

Steps to reproduce:

0. Set your browser's preferred language to Simplified Chinese
1. Find a documentation link without a specified language, like "Terms of Service" at /wp-admin/admin.php?page=wc-admin&path=%2Fpinterest%2Flanding. Or simply go directly to https://business.pinterest.com/business-terms-of-service/

Expected behavior

You should land on https://business.pinterest.com/zh/business-terms-of-service/ (The page is accessible from a browser with the preferred language set to English)

Actual behavior

There is a loop of redirects, which ends at 404

Additional details:

1. I tried a few other languages that work: Japanese, Polish - both work as expected.
2. We could do a short-term workaround, and hardcode /en/ for every link, but I believe that impairs the experience for other languages, and for Simplified Chinese users when the bug is fixed on the Pinterest end.
3. Personally, I think that should be fixed on the Pinterest end. //cc @jconroy

[jconroy]

@niketpins fyi for thoughts on how we should handle