@java.lang.Override
  public java.lang.String getSourceLanguageCode() {
    java.lang.Object ref = sourceLanguageCode_;
    if (ref instanceof java.lang.String) {
      return (java.lang.String) ref;
    } else {
      com.google.protobuf.ByteString bs = (com.google.protobuf.ByteString) ref;
      java.lang.String s = bs.toStringUtf8();
      sourceLanguageCode_ = s;
      return s;
    }
  }
<pre>
Optional. The ISO-639 language code of the input text if
known, for example, "en-US" or "sr-Latn". Supported language codes are
listed in Language Support. If the source language isn't specified, the API
attempts to identify the source language automatically and returns the
source language within the response.
</pre>

<code>string source_language_code = 4 [(.google.api.field_behavior) = OPTIONAL];</code>

@return The sourceLanguageCode.
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/TranslateTextRequest.java