"يَلّا مَعَ ٱلْسَّلامة!"
The makers of the course aren't trying to teach pure MSA here. They're trying to strike a balance between MSA and spoken language. As they mentioned in an article linked during the course launch:
we’re teaching a less-formal, spoken version of Modern Standard Arabic — not the version that would appear in poetry or formal news broadcasts, but instead the version that would be used once a newscaster stopped reading from their script and started talking to their interviewee. It’s a version of the language that can be used in a formal conversation, but one that also can be used with the widest range of Arabic speakers.
You can read their full article here https://making.duolingo.com/what-makes-arabic-hard-and-why-that-shouldnt-stop-you-from-learning-it
You wouldn't find يلّا in any Arabic text, هيّا is the closest term to mean the same thing.
yalla (يلا) is a colloquial abbreviation of 2 words : ya ( يا) , allah (الله) which means "oh allah" , which could be used to ask help from God or ask for his blessings to do a certain thing. With time, the usage of the phrase developed to indicate more meanings, like asking someone to initiate a certain action as in "come on do it.."; "يلا اعملها". It could also be used to say goodbye like the sentence above. And in rare occasions it could be used to express desperation in certain situations as in "whatever, it's all gone" ; "يلا كلو رايح" .
This word is "Yalla" and it means something along the lines of "c'mon" or "let's go" or "alright" in spoken language.
We use the word يَلّا regularly in everyday speech in Hebrew. It means let's do it, do it, let's go, etc.
yalla ( يلا)does not mean ALRIGHT, it means LET'S GO
a more accurate word would be Tayyib (طيب) or Hasanan (حسناً)
When يلا is taken in isolation, you’re right. But if you’re trying to translate the expression as a whole from Arabic to English, it would make sense to use “Alright” in this case. Duolingo favors equivalent expressions rather than word-for-word literal translations.