[Решено] Custom locale and migrating translations between locales

Background of the issue:
We need to create a custom locale for our English version of our German site (/de/en). It was set up using en_US, which is also used for our US site (/us), causing SEO issues in US Google search. We want to use en_EU instead for the English version of the German site. According to WPML documentation, we can create a custom locale and set it to English.

Symptoms:
Using en_US for both the German and US sites is causing SEO to show the wrong language in US Google search.

Questions:
If we create a custom locale en_EU, can we migrate all translations from the en_US locale to en_EU?
Is this something you can assist with?