The code is on a git repo linked at the bottom of the page.
The interface is in Slovene, but code and README are in English. The interface is using preprocessor strings, defined in src/i18n.h, which can be edited.
I'm requesting the very lightweight WAP website for the Nokia 6020 mobile phone. When I used this phone, I noticed Google sent a more lightweight page, but that was sometimes still too much for the phone to handle.
Later on, I added h=yes&l=20 parameters for using this specific phone, so that links are rewritten to HTTP from HTTPS (which is unsupported on the phone) and limited to 20 results, because the phone can't handle that big of a website.
Soon after I just went back to using a smartphone (: