Hello,
sorry for the late reply. Texts like {lang/join} or {lang/compress} appear when PDF24 cannot read its language files. They are in the subfolder lang of the PDF24 installation folder.
Please check that this folder exists, contains the .lang files and can be read by all users (security software may also block it). Version 11.9.0 is quite old, so the best way is to uninstall PDF24 and install the current version: https://tools.pdf24.org/en/creator
If the texts are still missing with the current version, please let us know.