In Discourse you can customize all of the text via the admin interface. Simply go to Admin > Customize > Text and you’ll be presented with a search page.
Search for the text you want to customize, click Edit then enter the new value. For example, I changed the “Dashboard” link to say “Evil Trout” here on Meta. After refreshing the page the text has been updated:
Need help identifying the strings to translate? See how to Find a translation key with verbose localization
As always, give it a spin and let us know of any bugs or suggestions and we’ll tweak accordingly!