Translation:Is it dark inside?
As many kanjis it has different readings,when used alone it uses its kunyomi pronounciation (naka), to make words the readings for 中 are なか ちゅう and じゅう (there might be special cases or more rare ones). With naka: tanaka (a surname) -> 田中, with chuu: chuushin (physical center) -> 中心, with juu-> ichinichijuu (~during all the day) 一日中. I'm not sure if it was related to your question but anyway, if you are new into kanji there are even easier examples, like numbers. When you refer to one or two (just the number) usually you say ichi or ni, but when counting things you say hitotsu (一つ), futatsu (二つ) that tsu is just a generic counter, as you might have seen (or will) here that changes depending o what you are counting (ej people: futari (二人)). Other common examples: 車 (~car) can be read as くるま or しゃ, when used alone (車) it's read kuruma (a car) , but then you have words like 電車: (electric) train which is read as densha