public Builder setLanguageCodeBytes(com.google.protobuf.ByteString value) {
      if (value == null) {
        throw new NullPointerException();
      }
      checkByteStringIsUtf8(value);
      languageCode_ = value;
      bitField0_ |= 0x00000001;
      onChanged();
      return this;
    }
<pre>
Optional. Recommended.
[BCP-47](https://www.rfc-editor.org/rfc/bcp/bcp47.txt) language tag.
If not specified, the API will return all supported voices.
If specified, the ListVoices call will only return voices that can be used
to synthesize this language_code. For example, if you specify `"en-NZ"`,
all `"en-NZ"` voices will be returned. If you specify `"no"`, both
`"no-&#92;*"` (Norwegian) and `"nb-&#92;*"` (Norwegian Bokmal) voices will be
returned.
</pre>

<code>string language_code = 1 [(.google.api.field_behavior) = OPTIONAL];</code>

@param value The bytes for languageCode to set.
@return This builder for chaining.
java-texttospeech/proto-google-cloud-texttospeech-v1/src/main/java/com/google/cloud/texttospeech/v1/ListVoicesRequest.java