The Sencha website is, in fact, the main resource for Ext JS and other Sencha products. Also this forum comes in Japanese and Portuguese.

The Sencha forum at http://www.sencha.com/forum/

This is the main page for Sencha, and it has forums for all its products, and also new releases. Premium forums are only for those who have a support subscription. The difference between premium forums and plain forums is that premium forums have a short response time.

ExtMX – the Spanish-language community for the Ext JS framework (http://extjs.mx/)

ExtMX is a Spanish-language community for the Ext JS framework, where they host tutorials. They also provide resources for courses or training. To access more features, you may need to create a user account (it's free).