Added support for the 'de-DE' language variant (informal) (#1008)

This commit adds support for the German language variant 'de-DE' in the application. The following changes were made:

Created the '/public/locales/de-DE/common.json' file for the 'de-DE' language
Modified the 'SwitchLang.tsx' component to include the 'de-DE' language option
Updated the 'localeText' function to display ' Deutsch' for 'de-DE'
These changes enable the application to provide localization in German for the informal 'de-DE' language variant. The newly created '/public/locales/de-DE/common.json' file contains the necessary translations for the German language. The 'SwitchLang.tsx' component has been updated to include the German language option ('de-DE') with the appropriate flag and language name.

Users can now select the informal German language ('de-DE') to interact with the application.

Co-authored-by: 🍌🐒 <nino@mohr.pw>

src/components/SwitchLang.tsx

@@ -17,6 +17,8 @@ const CustomLink = ({ href, children, as, locale, ...props }): JSX.Element => {
 
 const localeText = (locale: string): string => {
   switch (locale) {
+    case 'de-DE':
+      return '🇩🇪 Deutsch'
     case 'en':
       return '🇬🇧 English'
     case 'es':