Add language support to Epub metadata and hyphenation logic

lib/Epub/Epub/hyphenation/Hyphenator.h

@@ -13,4 +13,7 @@ class Hyphenator {
   // Returns byte offsets where the word may be hyphenated. When includeFallback is true, all positions obeying the
   // minimum prefix/suffix constraints are returned even if no language-specific rule matches.
   static std::vector<BreakInfo> breakOffsets(const std::string& word, bool includeFallback);
+
+  // Provide a publication-level language hint (e.g. "en", "en-US", "ru") used to select hyphenation rules.
+  static void setPreferredLanguage(const std::string& lang);
 };