GWT-maven-plugin can run the GWT i18n interfaces generator for your messages bundles. To enable this feature, simply include the i18n goal in your pom.xml:

<project>
  [...]
  <build>
    <plugins>
      [...]
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>gwt-maven-plugin</artifactId>
        <version>1.1</version>
        <executions>
          <execution>
            <goals>
              <goal>i18n</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <i18nMessagesBundle>com.mycompany.gwt.Bundle</i18nMessagesBundle>
        </configuration>
      </plugin>
      [...]
    </plugins>
  </build>
  [...]
</project>

If your application uses more than one bundle, you can nest multiple i18nMessagesBundle elements:

<project>
  [...]
  <build>
    <plugins>
      [...]
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>gwt-maven-plugin</artifactId>
        <version>1.0</version>
        <executions>
          <execution>
            <goals>
              <goal>i18n</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <i18nMessagesBundles>
            <i18nMessagesBundle>com.mycompany.gwt.Bundle1</i18nMessagesBundle>
            <i18nMessagesBundle>com.mycompany.gwt.Bundle2</i18nMessagesBundle>
            <i18nMessagesBundle>...</i18nMessagesBundle>
          </i18nMessagesBundles>
        </configuration>
      </plugin>
      [...]
    </plugins>
  </build>
  [...]
</project>

You can use the i18n goal to generate interfaces for either Messages, Constants and ConstantsWithLookup interfaces, using the associated i18nMessagesBundles, i18nConstantsBundles and i18nConstantsWithLookupBundles parameters