Making a case for english codebase to my boss

Hi people :)

I wanted to ask for your advice on a thing that I'm currently struggling with at my job.

For a little context, I'm a web developer from Chile, and currently, I'm in charge of maintaining a very old vanilla PHP codebase. (How old you say? It still has a JSON.php and a PHP4 HTML parser libraries on its assets that I just can't bear to delete from pure nostalgia. Lucky for me the code was barely refactored previously so It works on PHP 7)

At the moment I managed to free some time so I can migrate this codebase to a Symfony project, but I'm having trouble trying to find "solid good reasons" to have the codebase entirely in English.

Before this job, I was pretty much used to have my both my code and comments completely in English, and now having to propose this change to the "brass" I find myself without a reason to make this language change other than the classical:

• "It´s the standard way"
• "It kinda makes sense, since the framework is in English"
• "No need to think on tilde characters" (My heart dies little by little every time I see a agno variable because we should not use año

To me, due to the circumstances, these reasons that make all the sense to me seem more like "aesthetic reasons" for this case, mainly because:

• It's very likely that the code won´t be made public.
• It's even more likely that the dev team will be all "Chilean Spoken Natives" (Mandatory "Chilean Spanish is a different Spanish" reference xd).

But still, deep in my heart, I know that at least the codebase should be in English :(

So I ask you, dear dev community :)

Have you ever had to make this choice?
What reasons drove you to start/change to an all English codebase?
has anyone failed on a similar issue? Why?

Thanks for taking the time to help me with this thing :)