［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>