Tested with both current User and Unstable images. After selecting the language from the Ubiquity language selector, the selected locale is not applied to the live environment, it is always in English. For a coherent user experience, the selected language should be applied, so that user would know what to do when booted into the environment.
Thank you for your bug report! However this bug report was created/provided previous to 01/01/2023 and also has not received any updates since before 01/01/2025. Unfortunately KDE neon no longer provides updates for anything older than noble 24.04 based edition's. Please upgrade to KDE neon noble and if you can reproduce the issue after upgrading to an active version, feel free to re-open this bug report. Thanks for understanding!