In reply to Douglas Griffin: I always thought a diphthong was where two vowel sounds merged into each other: as in "oil", but not as in "bear", where there is only one vowel sound.
Scots and Yorkshire pronunciation has few diphthongs. Both tend to use pure vowel sounds (Yorkshire being even purer than Scots, I hate to admit) - also called monophthongs. Although few vowel sounds are totally pure.
Received English pronunciation and, say, London dialect are full of diphthongs. E.g. "oh no" in a mock upper class accent would have very distinct multiple vowel sounds, perhaps even more than 2! Or, in London, "south" can sound more like "sa-iff".
German has generally pure vowel sounds, not diphthongs. "Ueber" in particular is a monophthong. It's a pure sound. Unlike "neu", which sounds like "boy" and is a diphthong.
But, I notice from looking round t'Internet, that opinions tend to be divided on this! Wikipedia, if you trust it, is clear that a diphthong is a "gliding vowel sound", where you move from one vowel to another.