Äuä
Bernese German
Said in the canton of Bern
Come on! Really?
Äuä is one of the surest words to give a Bernese speaker away: Wikipedia counts it among the shibboleths of Bernese German, the words that tell where a speaker comes from. Its two syllables hide a long story. According to the Schweizerisches Idiotikon, the great dictionary of Swiss German, it goes back to Middle High German allewëge, which meant “always”. Elsewhere in German-speaking Switzerland the ancestor became allwäg, “probably, no doubt”. The Bernese, the Idiotikon notes, prefer the reduced form äuä; and in Bernese, as Wikipedia points out, the l is often pronounced like a u, which would explain that u.
The word does two jobs. Slipped into a sentence, it says you are fairly sure: “surely, no doubt”. Said on its own, as a reply, it took on an ironic turn over time, and that is the game’s sense: “come on!”, “really?”. Depending on the tone, it ranges from flat disbelief to mild surprise.
Interlaken is a special case. According to Wikipedia, that l turned u is a feature of the Bernese spoken on the Swiss Plateau, missing in the Oberland. The Idiotikon indeed quotes the people of Interlaken with a clear l: for them, the same old root gives albe, “in the old days”. Äuä is a word of the canton; these two clues suggest it is heard mostly on the Plateau, but none of the sources consulted says so.
To doubt a piece of news that sounds too good, or to say you are almost sure of something:
Sources: Schweizerisches Idiotikon, “Isch es äuä amig albig besser gsy? Äuää!” (Christoph Landolt, 2017); German Wikipedia, “Berndeutsch”; English Wikipedia, “Bernese German”.