I’m sure you’ll be a good help to the Dutch translation team!
Just a quick note on me, I am the one responsible for most of the German translation.
Let me give you a tip before you get started,
Some people try translating things without considering the context.
For example: “bookmark page” would become a literal page about bookmarks in translation (which you don’t want to have, obviously).
Sometimes you will have situations, where the translation can be understood, but doesn’t sound natural.
Let me give you another example:
“Ad Block” would translate to “Werbeblocker” in German, which nobody ever says, so I used “Adblocker” instead, which is how it’s commonly referred to in Germany.
Oh, and be sure to check your translations by using them (translations are only updated each new release).
One last thing:
When you’re having trouble understanding the context (which you will, believe me), asking for help is going to be very difficult, as apparently Brave doesn’t care about their translation at all, since they do not have anyone maintaining the issues (=comments or questions) on Transifex – which is the service used for translating by the way.
You can get started over on https://www.transifex.com/brave/brave-laptop/ for the Windows version.
I’m not sure about the iOS translation, because it was renamed to “iOS old”, which implies it’s no longer used.
I hope I was able to help you.