The translation used is the one that the user's browser requests. For the Pressero sites this can be overridden by changing the culture settings for the specific site, but all of the other sites without the culture change will obey the browser.
You can override your browser by telling it to request pages in English. The procedure differs depending on which browser is in use. Here is a somewhat old description:
Here is a somewhat more recent but more technical description:
So, the translations you created for the customer sites is not what is driving the translation you are seeing in the admin area... that is coming from your actual browser settings.