In the tellico windows version of KDE binary factory, no translation except English can be chosen in tellico.
From what I can tell, the nightly windows builds do not pull translations. https://www.mail-archive.com/kde-windows@kde.org/msg08980.html That's just an aspect of the KDE BinaryFactory nightly builds, unfortunately. Once windows builds from released packages are available, they will include translations
With the contributed installer for Tellico 3.4.4, it appears translations are available in the installation. https://tellico-project.org/tellico-3-4-4-for-windows/