Add words translation

Please clarify what you mean
> the plugin does not translate every single word.

For example the word “Enrolled” translated only in Germany but I want the translation in other languages too.

Is the word “Enrolled” in the theme template file?
Like this _e('Enrolled', 'theme-text-domain');

where can i find if it is?

Try check out files of your active theme.

No it doesn’t.
It is a word from another plugin. LearnDash

Maybe you need to ask LearnDash developer.