During the creation of a layout handle you specify a node
<label> which is some text to describe the layout handle. For example the layout handle
catalog_category_default has the following defined.
<label>Catalog Category (Non-Anchor)</label>
As part of the layout handle you can specify to translate these labels
<catalog_category_default translate="label">. Which makes sense if these labels are shown some place but I am not sure if or where they are shown to a user and so would require translation.