Still shown in English: suboptimal experience description

Playing with the values of OPTIMAL_BROWSERS in interface_config.js which works in general).
If I use a brwoser not listed in OPTIMAL_BROWSERS I get a “Browser Warning” window. This text is localised in lang/main-*.json, my setup is to detect German as client language, which generally works.
The title of the above mentioned warning is shown in German like expected, but if I expand the window the text explaining the warning still is in English (though I find a translation in lang/main-de.json).

Any hints how to setup this correctly?

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