Make Translate auth documentation clear and consistent

Additional updates prompted by googleapis#1594 / googleapis#2147.

README.md

@@ -177,7 +177,7 @@ Storage storage = StorageOptions.getDefaultInstance().getService();
   ```
 
 If no credentials are provided, `google-cloud` will attempt to detect them from the environment
-using `GoogleCredentials.getApplicationDefault()` which will search for Default Application
+using `GoogleCredentials.getApplicationDefault()` which will search for Application Default
 Credentials in the following locations (in order):
 
 1. The credentials file pointed to by the `GOOGLE_APPLICATION_CREDENTIALS` environment variable
@@ -497,8 +497,8 @@ Google Cloud Language (Beta)
 
 ### Preview
 
-Here is a code snippet showing a simple usage example of LanguageServiceClient. The example assumes that either default application
-credentials or a valid API key are available. (See [Authentication section](#authentication) for more information)
+Here is a code snippet showing a simple usage example of LanguageServiceClient. The example assumes that either Application Default
+Credentials or a valid API key are available. (See [Authentication section](#authentication) for more information)
 ```java
  try (LanguageServiceClient languageServiceClient = LanguageServiceClient.create()) {
    Document document = Document.newBuilder().build();
@@ -515,7 +515,7 @@ Google Cloud Vision (Beta)
 ### Preview
 
 Here is a code snippet showing a simple usage example of ImageAnnotatorClient.
-The example assumes that either default application credentials or a valid API key
+The example assumes that either Application Default Credentials or a valid API key
 are available. (See [Authentication section](#authentication) for more information)
 ```java
  try (ImageAnnotatorClient imageAnnotatorClient = ImageAnnotatorClient.create()) {
@@ -731,8 +731,8 @@ Google Translation (Beta)
 #### Preview
 
 Here's a snippet showing a simple usage example. The example shows how to detect the language of
-some text and how to translate some text. The example assumes that either default application
-credentials or a valid API key are available. An API key stored in the `GOOGLE_API_KEY` environment
+some text and how to translate some text. The example assumes that either Application Default
+Credentials or a valid API key are available. An API key stored in the `GOOGLE_API_KEY` environment
 variable will be automatically detected. Complete source code can be found at
 [DetectLanguageAndTranslate.java](./google-cloud-examples/src/main/java/com/google/cloud/examples/translate/snippets/DetectLanguageAndTranslate.java).
 
@@ -764,8 +764,8 @@ Google Cloud Speech (Alpha)
 
 ### Preview
 
-Here is a code snippet showing a simple usage example of SpeechClient. The example assumes that either default application
-credentials or a valid API key are available. (See [Authentication section](#authentication) for more information)
+Here is a code snippet showing a simple usage example of SpeechClient. The example assumes that either Application Default
+Credentials or a valid API key are available. (See [Authentication section](#authentication) for more information)
 Note that you must provide a uri to a FLAC audio file to run this.
 
 ```java
@@ -794,8 +794,8 @@ Google Cloud Trace (Alpha)
 
 ### Preview
 
-Here is a code snippet showing a simple usage example of TraceServiceClient. The example assumes that either default application
-credentials or a valid API key are available.
+Here is a code snippet showing a simple usage example of TraceServiceClient. The example assumes that either Application Default
+Credentials or a valid API key are available.
 Note that you must [supply credentials](#authentication) and a project ID if running this snippet elsewhere.
 ```java
  try (TraceServiceClient traceServiceClient = TraceServiceClient.create()) {
@@ -812,8 +812,8 @@ Google Cloud Video Intelligence (Alpha)
 
 ### Preview
 
-Here is a code snippet showing a simple usage example of TraceServiceClient. The example assumes that either default application
-credentials or a valid API key are available.
+Here is a code snippet showing a simple usage example of TraceServiceClient. The example assumes that either Application Default
+Credentials or a valid API key are available.
 Note that you must [supply credentials](#authentication) and a project ID if running this snippet elsewhere.
 ```java
 try (VideoIntelligenceServiceClient videoIntelligenceServiceClient =

google-cloud-examples/src/main/java/com/google/cloud/examples/translate/snippets/DetectLanguageAndTranslate.java

@@ -37,8 +37,9 @@ public class DetectLanguageAndTranslate {
   public static void main(String... args) {
     // Create a service object
     //
-    // Requests are authenticated using default application credentials if available; otherwise,
-    // using an API key from the GOOGLE_API_KEY environment variable
+    // If no explicit credentials or API key are set, requests are authenticated using Application
+    // Default Credentials if available; otherwise, using an API key from the GOOGLE_API_KEY
+    // environment variable
     Translate translate = TranslateOptions.getDefaultInstance().getService();
 
     // Detect the language of some text

google-cloud-translate/README.md

@@ -80,7 +80,7 @@ section to add `google-cloud-translate` as a dependency in your code.
 
 #### Creating an authorized service object
 To make authenticated requests to Google Translation, you must create a service object with
-credentials or with an API key. The simplest way to authenticate is to use
+credentials or use an API key. The simplest way to authenticate is to use
 [Application Default Credentials](https://developers.google.com/identity/protocols/application-default-credentials).
 These credentials are automatically inferred from your environment, so you only need the following
 code to create your service object:
@@ -142,8 +142,8 @@ Translation translation = translate.translate(
 
 In
 [DetectLanguageAndTranslate.java](../google-cloud-examples/src/main/java/com/google/cloud/examples/translate/snippets/DetectLanguageAndTranslate.java)
-we put together all the code shown above into one program. The program assumes that either default
-application credentials or a valid api key are available.
+we put together all the code shown above into one program. The program assumes that either Application
+Default Credentials or a valid API key are available.
 
 Troubleshooting
 ---------------

google-cloud-translate/src/main/java/com/google/cloud/translate/package-info.java

@@ -18,14 +18,15 @@
  * A client to Google Translation.
  *
  * <p>Here's a simple usage example for using google-cloud. This example shows how to detect the
- * language of some text and how to translate some text. The example assumes that the
- * {@code GOOGLE_API_KEY} is set and contains a valid API key. Alternatively, you can use
+ * language of some text and how to translate some text. The example assumes that either Application
+ * Default Credentials are available or that the {@code GOOGLE_API_KEY} environment variable is set
+ * and contains a valid API key. Alternatively, you can use
+ * {@link ServiceOptions.Builder#setCredentials setCredentials} to set credentials, or
  * {@link com.google.cloud.translate.TranslateOptions.Builder#setApiKey(java.lang.String)} to set
- * the API key. For the complete source code see
- * <a href="https://github.com/GoogleCloudPlatform/google-cloud-java/tree/master/google-cloud-examples/src/main/java/com/google/cloud/examples/translate/snippets/DetectLanguageAndTranslate.java">
- * DetectLanguageAndTranslate.java</a>.
- * <pre> {@code
- * Translate translate = TranslateOptions.getDefaultInstance().getService();
+ * an API key. For the complete source code see <a
+ * href="https://github.com/GoogleCloudPlatform/google-cloud-java/tree/master/google-cloud-examples/src/main/java/com/google/cloud/examples/translate/snippets/DetectLanguageAndTranslate.java">
+ * DetectLanguageAndTranslate.java</a>.  <pre>
+ * {@code Translate translate = TranslateOptions.getDefaultInstance().getService();
  *
  * Detection detection = translate.detect("Hola");
  * String detectedLanguage = detection.getLanguage();