i18n lang detection: remove language variant from detected langs

If the browser reports en-US as the preferred language that was
previously disregarded since it doesn't match any translations. This fix
strips off the variant, i.e. the part after the dash, so en-US becomes en.

Fixes #94

Author: rickard-von-essen

src/renderer/i18n/config.ts

@@ -38,6 +38,9 @@ void i18n
       // so we have to not keep any of the basic html nodes
       transKeepBasicHtmlNodesFor: [],
     },
+    detection: {
+      convertDetectedLanguage: (lng: string) => lng.split("-")[0],
+    },
   });
 
 export default i18n;