OnDemand uses the language packs generated from Atlassian and community support translations. I'm not sure if you're suggesting missing translations, or corrections, but you can contribute them for all to use.
I can confirm if you update your default language via 'System' > 'Edit Settings' and updating 'Default Language' to Espanol you will see Issue represented as Incidencias.
The issue type, 'Task'/'Tarea' will require configuration as discussed in https://confluence.atlassian.com/display/JIRA/Translating+Resolutions,+Priorities,+Statuses+and+Issue+Types
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