I can't seem to change the language during the conversation. I tried: <pre class="prettyprint"><code><speak> <voice gender="male" variant="3" langaugeCode="fr"> <prosody rate="105%"> Bonjour </prosody> </voice> </speak> </code></pre> Any ideas how to do that?

The <code><voice></code> tag is not officially supported in the SSML for the Google Assistant, although it does appear to partially work. Although the <code>gender</code> and <code>variant</code> attributes do appear to work, the SSML spec does not define a <code>languageCode</code> attribute (which you ask about in your question), and the <code>languages</code> attribute does not appear to be supported.

SSML Actions on Google, change speaking language

I can't seem to change the language during the conversation. I tried:

<speak>
<voice gender="male" variant="3" langaugeCode="fr">
<prosody rate="105%">
Bonjour
</prosody>
</voice>
</speak>

Any ideas how to do that?

The <voice> tag is not officially supported in the SSML for the Google Assistant, although it does appear to partially work.

Although the gender and variant attributes do appear to work, the SSML spec does not define a languageCode attribute (which you ask about in your question), and the languages attribute does not appear to be supported.