Hi @Zigor, thanks for the post and welcome.
Kindly make sure that your translations are organized in the correct folder structure under /public/locales . For example, you should have folders like /public/locales/en and /public/locales/es with the translation files inside.
If the above does not work, you can go to the Official Astro GitHub issues page below and then try to also get help there.
I got the SSR working adding the files as resources in the astro-i18next.config file:
import en from ‘./public/locales/en/translation.json’ assert { type: ‘json’ }
import es from ‘./public/locales/es/translation.json’ assert { type: ‘json’ }