According to this comment:
https://marc.info/?l=kde-i18n-doc&m=152672268226040&w=2
TRANSLATION_DOMAIN in CMakeLists.tx is not enough to make QML code translatable.
This can be easily tested using Neon:
https://files.kde.org/neon/images/neon-devedition-gitunstable/current/
This revision is trying to mitigate this issue with minimal changes in the code.