public Builder setSourceLanguageCodeBytes(com.google.protobuf.ByteString value) {
      if (value == null) {
        throw new NullPointerException();
      }
      checkByteStringIsUtf8(value);
      sourceLanguageCode_ = value;
      bitField0_ |= 0x00000004;
      onChanged();
      return this;
    }
<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>

@param value The bytes for sourceLanguageCode to set.
@return This builder for chaining.
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/TranslateTextRequest.java