Why is 中 pronounced like "なか"
Why is 中 pronounced like "なか" but it uses ちゅう?
Both are readings for that kanji.
The Kun-yomi (native Japanese) reading is なか - this is the reading that the kanji takes when it is by itself or a part of a person's name (with some exceptions). 中 means "middle/inside"
The On-yomi (Sino-Japanese) reading is ちゅう and is the sound the Kanji takes when used when combined with other kanji. (with some exceptions).
Duo is trying to teach you the on-yomi reading as it relates to 中国 "chuugoku" China, or 中学 "chuugaku" middleschool but Duo's system isn't capable of distinguishing the context the question wants you to use the kanji in so it always pronounces it with it's kun-yomi reading なか instead. Ideally I think the question should be changed so the hiragana fits the kun-yomi reading in the future, or at least explained a bit better in the course.
This gets worse with other Kanji that have multiple different readings. 日 has 17 different readings but Duo will always pronounce it with the single reading "ひ" when it is on its own and when you click on it in a word bank. Even though almost none of the questions require that reading. 今日は日曜日です "today is sunday" "kyou wa nichi you bi desu" uses the kanji for 'day' three times pronounced in three different ways. In a full sentence Duo will read it correctly, but if you're selecting each kanji one at a time you're going to be told "ima hi ha hi you hi desu"
I look forward to when they can engineer an update to the Incubator that can fix this. Though, I know they struggled already with getting the Incubator to the point it is with Japanese.
Btw, welcome! Thank you for volunteering to moderate. Your explanation above was clear and appreciated! :)
Thank you! Glad to be a part of the team! :)
I imagine trying to work around some of the incubator's limitations must drive the contributors mad, lol. Japanese sure is a beast of a language to program.