Deleted language ghost content

I started to set a site main config with French as default language and English as a supplementary language. Then I wanted to reverse the language priority with English as default and French as supplementary. But in D8, it seems there’s no way to change a site config language source and in my case, it remains hard coded to French. I even tried to completely remove the French language, but the config language source keeps showing French even if the language doesn’t exist anymore, cf screenshot.

One more info: I started to struggle in changing all these language settings because the original site name “Drupal” set in the English language could never get changed and because I found as well no way to have the front page selection get localized..

Could somebody give me some clue please on how to reset the D8 localization system (which seems not exactly ready for a production site) ?

Thanks in advance for any help 🙂

Only local images are allowed.   https://gyazo.com/8ff942f855fc9deaa574c0552fdfa0da

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