Language, appearance, and the update check
Settings is in the SaltPrint menu on a Mac — where macOS keeps it — and under File on Windows. Same window either way.
English, French, Italian or Spanish. Each language is listed in itself, so someone who can't read the current one can still find their own.
If you've never chosen, SaltPrint follows the language your computer is set to, and falls back to English for anything it doesn't have.
A few things stay in English on purpose: your own curve names are your words and are left exactly as you typed them, rubylith keeps its name because that's what the product is called, and file names never change with the language — so switching languages can't strand a curve or a saved setting.
Dark, Light, or Match system. Dark is the default, and stays the default unless you say otherwise — updating SaltPrint won't restyle an app you were happy with.
The image preview stays dark in both themes. That's deliberate, not something left undone: a pale surround around a dark negative makes it look denser than it really is, and judging density by eye is exactly the mistake this app exists to help you avoid.
Whether SaltPrint checks for a newer version when it launches. That check is the only request it makes that you didn't ask for, and you can switch it off here. What it sends, and what it doesn't, is on what leaves your computer.
Language and appearance apply the next time SaltPrint opens, and the app says so when you change one. That isn't laziness — the interface is built once at launch, so re-labelling or re-colouring it in place isn't something it can do honestly.