I’ve stumbled across this in written English many times – for when somebody wants to announce “there it is”, English borrowed the French word “voila” (not to be confused with a “viola”, the stringed instrument one size larger than a violin). “Voila” literally means “see there”, and comes to mean “there it is” or, more idiomatically, “there you have it”.
An example usage might be “I couldn’t find my glasses, until I checked my head – and voila! There they were.”
However, since it is a word you rarely see written out – and being French has a slightly unexpected spelling for English speakers – people have been spelling it somewhat phonetically, resulting in the word being seen as “walla” or “wallah”. While both of these words do exist, their meanings are very different from the intended “voila”.
“Walla” is a word used in American English to describe the background noise of a crowd murmuring, usually on a movie set. It’s called such because moviemakers discovered that background actors could easily recreate the sound of background conversation just by repeating the word “walla” over and over again to each other. There are different variations of this in different countries – in the UK they use the word “rhubarb”, in Germany “rabarber”, and in Japan “gaya”.
“Wallah” is also an Arabic word meaning something along the lines of “really”, and is used when a speaker wants to express that what they are saying or what they have just said is indeed true. It’s literal meaning is “(I swear) by Allah”.
So there you have it. If you want to say “there it is”, use voila. If you want to mimic the background noise of American English speakers in conversation, use walla. And if you want to declare that something is the truth in Arabic, use wallah.
Et voila! There you have it.