Specific Nightingale advise coming soon…
Meanwhile feel free to check out generic advise freely available online, for example Canonical's Launchpad Help, a summary of the main points are presented below:
Below are listed some commonsense rules to follow during the translation work in order to improve the translation quality:
This section contains general information about strings that should not be translated and how to identify them.
Whilst translating Nightingale you may come across placeholders such as %S or %1. You may also see more complex variations, such as &(variablename). Copy these variables and placeholders exactly as you see, placing them in the exact order in whichever part of the string makes most sense in the target language. If you're in doubt, ask another translator for advice.
Would you like &brandShortName; to scan your new watch folder: (%1$S)?
In some languages translators agreed to specific guidelines. Please check the languages thread in this subforum for those guidelines.