Capitalize language name according to selected locale

.changeset/yummy-donkeys-repair.md

@@ -0,0 +1,5 @@
+---
+'@theoplayer/web-ui': patch
+---
+
+Language names in the language menu are now capitalized according to that language's case mappings.

src/util/CommonUtils.ts

@@ -106,7 +106,9 @@ export const localizeLanguageName: (languageCode: string) => string | undefined
               const displayNames = new Intl.DisplayNames([languageCode, 'en'], { type: 'language', fallback: 'none' });
               const localName = displayNames.of(languageCode);
               if (localName) {
-                  return localName.slice(0, 1).toUpperCase() + localName.slice(1);
+                  const locale = displayNames.resolvedOptions().locale;
+                  const [first] = localName;
+                  return first.toLocaleUpperCase(locale) + localName.slice(first.length);
               }
           }
         : (_languageCode) => undefined;