Fix: Auto language detection #2122 (#2148)

* Fix: Auto language detection #2122

* add LanguageService and AdditionalLanguageJsController

* hidden swagger

src/main/java/stirling/software/SPDF/service/LanguageService.java

@@ -0,0 +1,41 @@
+package stirling.software.SPDF.service;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
+import org.springframework.stereotype.Service;
+
+@Service
+public class LanguageService {
+
+    private final PathMatchingResourcePatternResolver resourcePatternResolver =
+            new PathMatchingResourcePatternResolver();
+
+    public List<String> getSupportedLanguages() {
+        List<String> supportedLanguages = new ArrayList<>();
+
+        try {
+            Resource[] resources =
+                    resourcePatternResolver.getResources("classpath*:messages_*.properties");
+            for (Resource resource : resources) {
+                if (resource.exists() && resource.isReadable()) {
+                    String filename = resource.getFilename();
+                    if (filename != null
+                            && filename.startsWith("messages_")
+                            && filename.endsWith(".properties")) {
+                        String languageCode =
+                                filename.replace("messages_", "").replace(".properties", "");
+                        supportedLanguages.add(languageCode);
+                    }
+                }
+            }
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+
+        return supportedLanguages;
+    }
+}