Translation doesn't work on breadcrumbs added by xml

To translate a crumb without using a helper, you can use the translate attribute for your action node by using crumbInfo.label and crumbInfo.title.

Exemple:

<reference name="breadcrumbs">
    <action method="addCrumb" translate="crumbInfo.label crumbInfo.title">
        <crumbName>home</crumbName>
        <crumbInfo>
            <label>Home</label>
            <title>Home</title>
            <link>/</link>
        </crumbInfo>
    </action>
    <action method="addCrumb" translate="crumbInfo.label crumbInfo.title">
        <crumbName>brands</crumbName>
        <crumbInfo>
            <label>All Brands</label>
            <title>All Brands</title>
        </crumbInfo>
    </action>
</reference>

It's the better way to translate breadcrumbs, use helpers only if you have the set a custom title depend on URL params or something else.

Note that you can also generate links for breadcrumbs using helper class.
Using helper class, above XML block may look like:

<brand_brand_index translate="label">
    <reference name="breadcrumbs">
        <action method="addCrumb">
            <crumbName>Home</crumbName>
            <params helper="module/getHomeUrl" />
        </action>
        <action method="addCrumb">
            <crumbName>All Brands</crumbName>
            <params helper="module/getBrandUrl" />
        </action>
    </reference>
    [[...]]
</brand_brand_index>

And add the getHomeUrl() & getBrandUrl() methods in your module's Helper/Data.php as:

class Namespace_Module_Helper_Data extends Mage_Core_Helper_Abstract
{
    //...

    public function getHomeUrl()
    {
        return array(
            'label' => Mage::helper('module')->__('Home'),
            'title' => Mage::helper('module')->__('Home'),
            'link' => Mage::getUrl(),
        );
    }

    public function getBrandUrl()
    {
        return array(
            'label' => Mage::helper('module')->__('All Brands'),
            'title' => Mage::helper('module')->__('All Brands')
        );
    }
}