Also can anyone explain why you need a ‘ber’ in the first place, what is the difference between ‘Saya jalan’ and ‘Saya berjalan’? It wasn’t clear to me in the intro...
(ber-) + (noun) = verb
The word "jalan" is a noun, so it needs the ber- prefix to use it as a verb (in the formal way).
"Saya jalan" is informal.
The word "jalan" is used as a verb in this sentence.
As you can see in the dictionary, it's only used as a verb in the informal way.
That's the reason the ber- prefix is used here.
I believe "he stands and walks" would work, but duolingo detects is as wrong.
Indeed. It's started off with only "stands up" sentences being accepted; I think for every "stands" sentence, we need to use the report button to get them accepted.
I guess the contributors had not considered that option. The course is still in Beta, so we need to use the report button to get the additional ways of saying things marked as correct.
I think the majority of the course contributors are native Indonesian speakers rather than native English speakers; and when they listed the possible correct translations the "stands" options got left out - I suspect they might have been taught to use "stands up" as the direct translation of "berdiri" to avoid confusion with "stands still". "Stands" on it's own can mean either, and should be valid here.
I'm not sure, to be honest, but when there's a couple of different senses to a word in English, there's often a fair chance that the concepts translate to entirely different words in other languages. Just guessing really.