I think I've found a decent solution. As @lyssipos explains, hreflang-tags in the body aren't of value to Google.
I used Gemini to write me some javascript that lets me add hreflang-tags to the header using codeblocks.
This is my code but bear in mind you're going to have to adjust it according to your website's structure, this is based on my site that uses subdirectories for /en and /sv:
function addHreflangTags() {
const currentURL = window.location.href;
// *** ADJUST: Extract the language code from your URL structure ***
const languageCode = currentURL.split('/')[3]; // Example, change the index if needed
// *** ADJUST: Your website's base URL ***
const baseURL = "https://www.example.com/";
const alternateLang = (languageCode === 'en') ? 'sv' : 'en';
const alternateURL = baseURL + alternateLang + currentURL.substring(baseURL.length + languageCode.length);
// Create links
const linkCurrent = document.createElement('link');
linkCurrent.rel = "alternate";
linkCurrent.href = currentURL;
linkCurrent.hreflang = languageCode;
const linkAlternate = document.createElement('link');
linkAlternate.rel = "alternate";
linkAlternate.href = alternateURL;
linkAlternate.hreflang = alternateLang;
const linkXDefault = document.createElement('link');
linkXDefault.rel = "alternate";
linkXDefault.href = baseURL + 'en' + currentURL.substring(baseURL.length + languageCode.length);
linkXDefault.hreflang = "x-default";
// Append links to the head
document.head.appendChild(linkCurrent);
document.head.appendChild(linkAlternate);
document.head.appendChild(linkXDefault);
}
window.onload = addHreflangTags;
