I can’t think of another language that uses it, and google yielded nothing.
It looks like [oʊ] is also found in some dialects of Dutch, Czech and Mandarin Chinese.
The only evidence I found for it being in Mandarin is the word for “mouth” (口) which is romanised as “kǒu”. Every audio I found pronounced it something more like “cow”, as in 
. I’m looking for languages that use the actual sound, regardless of how they write it.
I will have a look at Czech and Dutch.
What do people in other countries say when you give them a Hertz Donut?
To save others the need to Google up IPA, this is what it sounds like in English:
oʊ = boat, owe, no
IPA is definitely a practical tool, but every time I see it used I feel I have to search for my secret decoder ring!
“Should have seen that coming.”
What about « l’eau » in French? Sounds like the same sound as « owe » but maybe that’s just my ears.
Tokyo? Sumo? Domo Arigato?
The French pronunciation of ‘eau’ is a single vowel IPA /o/. The sound described by the OP a combination of two vowels, /o/ followed by /ʊ/.
That’s just in the English versions of those words. IMHO the Japanese vowels sound very similar to Spanish vowels. Think of those words as a native Spanish speaker would pronounce them, and they sound a lot closer to how they do in Japanese compared to the English pronunciations. At least to my ears.
I can confirm that is correct.
A language that uses [oʊ] very often is Galician (spoken in North-Western Spain, the square above Portugal), it is one of its most characteristic phonemes. The capital city of one of its four provinces is called Orense in Spanish, Ourense in Galician. The “Ou” in Ourense is pronounced exactly like [oʊ] in the English words minor7flat5 gave as an example: boat, owe, no.
I guess Portuguese also uses that sound, some dialects of Portuguese are almost indistinguishable from Galician.
In Mandarin it is indeed the oʊ sound. What might be deceiving you in hearing 口 is the drawn-out third tone, which I see tends to be exaggerated in pronunciation guides. Try listening to 头 (head) which is the same vowel in second tone. Google translate has good natural-sounding pronunciations of Mandarin.
That strikes me as badly wrong, regardless of where you found it listed that way. Although of course that’s based on how I pronounce (and hear others pronounce) those three words.
If I were writing IPA for those words I would use the pure “o” character for all three.
The diphthong oʊ is the combo of the pure “o” sound and the “ʊ” sound which is generally described as the vowel you hear in the English words “book” and “look” and “cook”.
The only words that immediately spring to mind as “oʊ” words are “boa” (like a boa constrictor or a feather boa) and the constellation Boötes.
I’m not sure what your accent is, but this page gives numerous examples of the oʊ sound that you can click on to hear. Most of these are US accents.
over, older, going, social, almost, also
(Among their examples older doesn’t sound quite like the oʊ sound to me, but it’s quite subtle.)
I’m an American (Midwesterner now living in the East) and I definitely pronounce this vowel as a dipthong.
If you speak Spanish, you can hear the difference between the /oʊ/ and a pure /o/ by comparing how ‘no’ is pronounced in the two languages. .
This is the one I used:
I don’t know IPA well enough to judge if their examples are incorrect.
Does “Hebrew, as spoken by most American Jews” count as a dialect?
Long “o” sounds, which effectively become “ou” are present in those words (not “sumo” though, I’m pretty sure) in the original Japanese, and lots of other words. Most non-native Japanese speakers who pronounce those words would just use short “o” because they don’t know which o’s are supposed to be long. “Domo” for example, spelled to emphasize pronunciation for English speakers, would be “doumo.”
Every single one of those I pronounce with the pure “o” (IPA) sound.
Hang on, I’m going to that site to see what they consider examples of “o” by itself in English…
… they don’t HAVE ANY???
That’s just weird. And wrong. ETA: or contrary to what I was taught at any rate.
But have you listened to the recordings? I don’t know what weirdass accent you have 
but the point of linking to the site was that we can all hear the oʊ sound without the unknown variable of our own accents that we can’t mutually hear. You do agree that what you hear on those recordings is the oʊ sound, correct? Otherwise that’s the source of the problem.