Groovy script to get translations using Google Translate API gives java.lang.NoSuchMethodError

Question

I am trying to write a Groovy script to get translations from Google Translate API (using an API key, stored in as the GOOGLE_API_KEY environment variable1) but I get an error I'm not able to overcome. The Groovy script runs in OmegaT, which is a Java application.

References: Google Translate's API documentation and the code in Google APIs' Github repo.

This is my script:

@Grapes([
    @Grab(group='com.google.cloud', module='google-cloud-translate', version='2.1.13')
])

import com.google.cloud.translate.Translate;
import com.google.cloud.translate.Translate.TranslateOption;
import com.google.cloud.translate.TranslateOptions;

// api key is stored in the GOOGLE_API_KEY environment variable 
Translate translate = TranslateOptions.getDefaultInstance().getService();

String translation = translate.translate("Hello world", 
          TranslateOption.sourceLanguage("en"), 
          TranslateOption.targetLanguage("es"));

console.println(translation); // "Hola mundo"

When I run the script I get the following error:

The script "/home/pico/.omegat/scripts/mt_google.groovy" is running...
An error occurred
java.lang.NoSuchMethodError: com.google.common.util.concurrent.MoreExecutors.directExecutor()Ljava/util/concurrent/Executor;

I've read online that this can be caused by a dependency conflict and that it might be related to guava. I have tried excluding that library like this (at the top of the script), but to no avail:

@GrabExclude(group='com.google.guava', module='guava')

Thanks in advance for any advice.

---

UPDATE:

From the source code folder of the Java application inside which my Groovy script runs I can generate a tree of Guava dependencies, like so:

> ./gradlew dependencies | grep guava
     +--- com.google.guava:guava:23.6-jre
|    |    +--- com.google.guava:guava:16.0.1
|    |    +--- com.google.guava:guava:16.0.1
|    |    |    \--- com.google.guava:guava:15.0 -> 16.0.1
|    |    +--- com.google.guava:guava:16.0.1
|    |    |    \--- com.google.guava:guava:15.0 -> 16.0.1
|    |    +--- com.google.guava:guava:16.0.1
|    |    +--- com.google.guava:guava:16.0.1
|    |    +--- com.google.guava:guava:16.0.1
|    |    +--- com.google.guava:guava:16.0

I can share the full list without grepping but it's a long list.

I have now tried with the following section at the top of my script:

@Grapes([
    @GrabExclude(group='com.google.guava', module='guava', version='16.0.1'),
    @Grab(group='com.google.cloud', module='google-cloud-translate', version='2.1.13')
])

but then I get error java.lang.NoClassDefFoundError: com/google/common/base/MoreObjects.