This thread is resolved. Here is a description of the problem and solution.
Problem:
If you're wondering whether WPML can display the US English variant of your website when a browser is set to US English (en-US), instead of the default English version.
Solution:
We confirm that WPML can indeed serve the US English variant if the browser language is specifically set to US English (en-US) and the US English variant is published and active on your site. If the browser language is set to English generally, it will default to the main English version of your site. We have tested this functionality on a fresh WP site and confirmed that it works as expected.
If this solution does not resolve your issue or seems outdated, we recommend checking the related known issues, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If further assistance is needed, please open a new support ticket.
This is the technical support forum for WPML - the multilingual WordPress plugin.
Everyone can read, but only WPML clients can post here. WPML team is replying on the forum 6 days per week, 22 hours per day.
This topic is split from https://wpml.org/forums/topic/links-on-the-us-english-variant-pages-redirect-to-the-default-english-variant-instead-of-the-us-engl/

