I use only one extension - ContactPage.
Using the template engine HTMLForms implemented as form-template for ContactPage I created a selection menu in my form.
The keys and values of this selection menu are written in English inside LocalSettings.php
But,
I would like them to appear in my site's native language for surfers.
I could translate these extensionless with JavaScript by some similar code:
document.getElementById('select').selectedIndex = 0;
document.getElementById('select').value = 'Default';
In the Drupal CMS for example, there is a "backend" internal translation mechanism that allows to do just that, but I don't know of a similar internal mechanism in MediaWiki.
I wonder how you would do it "backend" and extensionless:
What are the possible ways to translate in MediaWiki without an extension?