［Google Translation API v2 for Java］

Reference:
https://cloud.google.com/translate/docs/reference/libraries#java-resources

QuickstartSample:

 // Imports the Google Cloud client library
 import com.google.cloud.translate.Translate;
 import com.google.cloud.translate.Translate.TranslateOption;
 import com.google.cloud.translate.TranslateOptions;
 import com.google.cloud.translate.Translation;

 public class QuickstartSample {
   public static void main(String... args) throws Exception {
     // Instantiates a client
     Translate translate = TranslateOptions.builder().apiKey("YOUR_API_KEY").build().service();

     // The text to translate
     String text = "Hello, world!";

     // Translates some text into Russian
     Translation translation = translate.translate(
       text,
       TranslateOption.sourceLanguage("en"),
       TranslateOption.targetLanguage("ru")
     );

     System.out.printf("Text: %s%n", text);
     System.out.printf("Translation: %s%n", translation.translatedText());
   }
 }

maven:

 <dependency>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-translate</artifactId>
     <version>0.4.0</version>
 </dependency>