21. The Uyghur vowel system may be subcategorized on the basis of height, backness and roundness. 22. The vowel system of Ormuri is characterized as heterogenous. 23. Two-vowel systems are very rare worldwide, but are also found in some Northwest Caucasian languages. 24. The northern dialect of Tukang Besi has 25 consonant phonemes and a basic 5-vowel system . 25. There is also a glottal phoneme,', and a three vowel system common in Australian languages. 26. Regarding phonology, there is also a seven-vowel system but the vowel harmony is not mandatory. 27. A widely used Roman character-based writing system is the Double Vowel system , attributed to Charles Fiero. 28. They have fairly simple phonologies and similar vowel systems , both marking length in consonants and vowels. 29. For most languages, the vowel system is triangular. 30. The Fas language apparently has a seven-vowel system .
