That language is not your own warning in red
Please add a button to get rid of it instead of googling the origin of the message, finding out it's ES and then finding the off switch.
So the entire point of warning people in English that they are not browsing in their own language is kinda stupid. If you don't understand English, then writing in English that it's not their language defeats the point of the warning. unless you want to troll people.
Then you succeeded.
I've edited your message to remove inappropriate language. This is your only warning for that infraction.
As for your complaint it seems that something didn't happen properly. The code is supposed to detect your native language when you first run Enhanced Steam, then warn you when you subsequently access Steam in another language. This is not an attempt to troll people, but an attempt to fix a legitimate problem where people inadvertently change their language on Steam and cannot figure out how to change it back (since the menus are then in another language).
I'll see what I can do about adding a "close" button to this, and an option along the lines of "don't show this again".
So, Enhanced Steam is discontinued. There is now Augmented Steam. Perhaps your requested feature/bugfix is already implemented there! If not, you could move your issue there.