Well, if you're developing a custom advanced workflow in Alfresco using Activiti you should check out this Jeff Pots guide.
Other than that, in order to use a customised string for your start event you should be familiar with content modeling and i18n properties files.
So for your startEvent you should have a specific workflow model declaring the workflowdocumentrequest:start type, something similar to this:
<type name="workflowdocumentrequest:start">
<parent>bpm:startTask</parent>
...
</type>
For that workflow content model you should have a specific i18n file, in messages folder called workflowdocumentrequestWorkflow.properties.
There you should have something like this:
workflowdocumentrequestWorkflow_workflowmodel.type.workflowdocumentrequestWorkflow_start.title=Início
The workflowdocumentrequestWorkflow_workflowmodel part is your namespacePrefixShortname_yourWorkflowModelName (the one you have used at the beginning of your workflow content model xml file <model name="workflowdocumentrequestWorkflow:workflowmodel xmlns="http://www.alfresco.org/model/dictionary/1.0">.
The .type. is obviously your custom type for the start event task.
The workflowdocumentrequestWorkflow_start is your type's name in your xml. Activiti engine and i18n file hase to be written with _ instead of :.
Hope it helps.
Cheers