Thanks for trying Gibbon! We apprciate any feedback for making it better.
for currency, we are working on a broader solution: but for now, you can go into gibbonSetting in the database and search for the currency field, and manually set the currency. It will be undone any time you edit System Settings, and may cause issues with PayPal. We are going to have a formal fix for this in Gibbon v9.1, which should be out in the next three months. For changing the other phrases, you can edit the language files for your language in /i18n. Again, this will be overwritten when you update to a new version of Gibbon, but is the only way to do it for now.