After using a localization plugin to add the French translation, the following warning showed up.
Warning: The actual loaded translation content contains mixed textdomains and is not pure translateable within one textdomain.
It seems, that there is code contained extracted out of other plugins, themes or widgets and used by copy & paste inside some source files.
The affected unknown textdomains are: debug page, category shortcode, add fee, Used for decimal separation: (The dot in 1,000.00).
Is there a way I can solve these problems?