Nor does Y-bar's example from EUR-Lex, where the language list is below the catalogue information. It being right at the top in a banner of hyperlinks with 2-letter codes is not actually a part of the pattern. The E.U. Parliament and E.U. Court of Justice use drop-down menus with the full language names, for example.
Well one is a random directive from 2022 about radio equipment marketing; and the other, hyperlinked by outadoc in the first place, was the very text of the European Union Public Licence version 1.2 as PDF and text/plain formats in 23 languages, with the EUPL version 1.1 as PDF in 22 languages at the bottom of the page.
If you wanted an apt one, instead of a random radio equipment marketing directive, that was specifically EUR-Lex, there's https://eur-lex.europa.eu/eli/dec_impl/2017/863/oj which is the E.U. Commission decision promulgating version 1.2 of the EUPL.
As noted elsethread, neither one, nor the E.U. Parliament nor E.U. Court of Justice, does things exactly the way that Javier Casares does them.
Also note that outadoc wasn't actually asking how to read the text, in the first place. outadoc was pointing out that Javier Casares's unofficial copy here does not anywhere hyperlink (in order to provide a source) to the official europa.eu. WWW site, which outadoc then pointed to. Nor does it hyperlink to the aforelinked E.U. Journal entry.
Like https://interoperable-europe.ec.europa.eu/collection/eupl/eu... as given above. (-: