[Feat]: Implement language selection

**😒 Is your feature request related to a problem? Please describe.**
There is currently no possibility to change the language of foxdeck, alltough we support the english language.

**🤔 Describe the solution you'd like**
The FDDropdown component should be used for implementation. This component accepts a list of elements (in our case a list of supported languages, i.e. German and English) as well as the currently selected element (the currently used language is obtained via the "useI18n" composable). If the language is changed, the newly selected language must be set (also via the "useI18n" composable).

The dropdown should be at the settings overlay on the top right of the application,

Start at the settings overlay and trace its FDDropdown usage and the useI18n composable; identify the existing supported-language data and selection state. Done means the overlay offers German and English, shows the current language, and changing the selection updates the application's language through useI18n.

Written by the indexing model from the issue text.