Your project language decides which language Steady uses when it writes to your members. You can choose German, English, French, Italian or Portuguese.
You set it in your backend under Settings → Project Settings, in the field Project language. Change your project language.
What the project language controls
The emails your members receive about their membership.
The standard text Steady adds to your post emails. Your own text stays exactly as you wrote it.
The emails Steady sends you about your project, e.g. when you get a new member.
Recommendations: when Steady automatically recommends other projects to your readers, it picks projects with the same project language.
What it doesn't change
Your Steady page and the checkout appear in each visitor's own language: the language they picked on Steady, or otherwise their browser language. If you want everyone to see one language, add the language code to your link, e.g. steady.page/de/yourproject – see Where do I find my Steady page and URL?
Your own texts – such as your project description, plan names and posts – are never translated automatically. They always appear as you entered them.