[Polylang] .mo file does not show up

Hello,

I translated my theme with Polylang from English (default) further into traditional Chinese (Taiwan) and have uploaded a .mo file to loco translate, which should normally get the hardcoded strings visible in the theme. I am using a child theme.

The Theme itself also uses a customizer and exactly those strings I translated with poedit/loco translate but they will not show up in the Chinese version. All the strings are still in English, when visiting the page.

The .po mo. files are are called and in /themename/languages/zh_TW

What can go wrong? How does Polylang connect with .mo files?

I searched for a long time but I cannot get this clear and really hope for an
answer.