"Is it dark inside?"
You don't see 内 used on its own very often, and even then it would probably sound as うち
I need help here, why aren't we using "ni" or "de" here as topic markers
「中は明るいか」should work? I don't like being polite all the time, but I don't know if there is something with the い-adj...
They're right, か can't just be tagged onto the end of an いadjective. If you don't want to use です then you also don't use か and raise your voice at the end to imply the question like we do in English. Since you can't convey tone in an app, you'll be using formal speech for a while...
If I'm not mistaken, I think it's more common to just use a rising intonation to form a question when using the plain conjugation as opposed to the formal!
Yeah, it would just be 「中は明るい」in that case. You need the desu if you add ka or it sounds wierd.
You can do it, it's fine grammar-wise. Though, you might go with のか instead, for no other reason that it would sound more amiable that way. It's an ARE YOU BEING BRIEF WITH ME kinda thing.