"He will go to the city tomorrow."
Translation:वह कल शहर जायेगा ।
It's also correct. However, Duolingo creators are not teaching other possible word orders. Note, Hindi is a word order free language (with the default word order being SOV). Often the word order of the sentence is switched to change the nuance of the sentence. For example,
- वह कल शहर जायेगा
- He will go to the city tomorrow.
- वह शहर कल जायेगा
- It is tomorrow (when) he'll go to the city.
- वह शहर जायेगा कल
- It is the city (where) he is going tomorrow.
- कल वह शहर जायेगा
- It is him (who) will go to the city tomorrow.
But, note you really don't have to get involved in learning what word order means what. Often there's no particular logic as to what a particular word order means. You can any word order and you'll be understood by a native, no issues. If you want to emphasise somett in the sentence without switching the word order you can just raise your intonation on the word. (Applies to whatever word order you speak in)
Also, I just changed the position of कल in the above sentence, you could switch any word with any other word in the sentence above and it'll still make sense, and it's very common that people often do not stick to SOV word order. For example, जायेगा शहर कल वो is also a valid sentence and you'll often hear it in colloquial speech.
जायेगा/जायेगी (jāyegā/jāyegī) and जाएगा/जाएगी (jāegā/jāegī) are synonymous. These days you'd see a lot of people omitting the य (y) sound if the vowels ए (e), ऐ (ai), इ (i) and ई (ī) follow it. Also, the vowel preceding य (y) must not be ए (e), ऐ (ai), इ (i) and ई (ī).
So, examples: (assume ऐ = «è»)
- āye / aye = āe / ae [valid]
- ūye / uye = ūe / ue [valid]
- eye / èyè ≠ ee / èè [invalid]
- iyi / īyī ≠ ii / īī [invalid]
Personal Opinion: However, it's often not skipped when writing Hindi in Latin script. So, jāegā/jāegī is often not written, instead always jāyegā/ī.