Language state lost by going back to the main page

[Damian-Oswald]

• If I'm on the main page (index.html), I can select the language correctly via the URL or the dropdown.
• If I'm on the main page and click the title of the page then the main page switches to English (this is unwanted) or even worse, to the placeholder names.
• If I'm on the main page and click on a dataset, the current language is correctly kept, also the state of the dropdown.
• If I click on the title, the main page is loaded but sometimes with English, sometimes with the placeholders. I have no idea why.