It's probably best classified as an interjection. You British have more complex ones than we do; you have things like "cor" while we limit ourselves mostly to pure vowels and semivowels like "wow." However, we both use profanity as interjections when we're really upset, as well as blasphemous religious terms. Sometimes all combined together into complicated polysyllabic constructions like g** d*** m***** f***ing s** of a b****, apparently one of the first phrases Americans learn as children.
Whether you call an interjection a "word" is a fine point and I don't know how the professionals rule on that. What matters in the context of translation is that interjections express feelings more than denotative meaning. Even the eight-word compound above means nothing except, "I'm feeling a lot of pain and/or anger."
The tell is that tone matters a lot with interjections. "Oh" can mean "now I understand," "I don't understand at all," "what a surprise," "I was expecting that," "I'd like to hear more about that," "I never want to hear about that again," and many other things, depending on the tone.
Your two-syllable interjection apparently has a specific meaning, but you make it clear that it has to bear a specific combination of tones in order to carry that meaning. Tone is not phonemic in English, so I'd be reluctant to classify it as a word.
As to whether it needs to be translated... hmm. With a rising tone on the short first syllable and falling tone on the longer second syllable, I feel like I would get the basic connotation of "now I understand," but the long "ah" with the falling tone does that all by itself. I would not pick up the subtleties you add.
So I don't think a speaker of another language would understand it fully. Still, I don't know how you would go about translating it. Every language community has different interjections.
Sitting here grunting to myself experimentally, providing my dogs with great entertainment, I think would probably express that sentiment using the same tones, but on a constant "oh," and about three times faster. And I would finish on a lower tone than I started. All right, let's take this to the piano. It's A, C, low E.
