In Zammad (as admin) you can translate strings having typos or even not being translated. You can always "Get last translations" to ensure that you're up to date before doing that.
Note: The language for translation is always the language you chose within your profile. As Zammad's main language is English, you can't translate into English.
Translated strings are highlighted within Zammad. If you've translated strings, you have two options: You can send your changes to our central system, this will share your translation with other users. This is a great contribution.
If you don't like your changes or want to start over, you can discard your changes at any time.