Phonotactics
Languages' phonotactics differ as to what consonant clusters they permit.
Many languages forbid consonant clusters altogether. Maori and Pirahã, for instance, forbid any two consecutive consonants in a word. Japanese is almost as strict, but allows clusters of consonant plus /j/ as in Tokyo, the name of Japan's capital city. Across a syllable boundary, it also allows a sequence of a nasal plus another consonant, as in Honshū (the name of the largest island) and tempura (a traditional dish). A great many languages are more restrictive than English in terms of consonant clusters; almost every Malayo-Polynesian language forbids consonant clusters entirely. Tahitian, Samoan and Hawaiian are all of this sort. Standard Arabic forbids initial consonant clusters and more than two consecutive consonants in other positions. So do most other Semitic languages, although Modern Israeli Hebrew permits initial two-consonant clusters (e.g. pkak "cap"; dlaat "pumpkin"), and Moroccan Arabic, under Berber influence, allows strings of several consonants. Like most Mon–Khmer languages, Khmer permits only initial consonant clusters with up to three consonants in a row per syllable. Finnish has initial consonant clusters natively only on South-Western dialects and on foreign loans, and only clusters of three inside the word are allowed. Most spoken languages and dialects, however, are more permissive. In Burmese, consonant clusters of only up to three consonants (the initial and two medials—two written forms of /-j-/, /-w-/) at the initial onset are allowed in writing and only two (the initial and one medial) are pronounced. These clusters are restricted to certain letters. Some Burmese dialects allow for clusters of up to four consonants (with the addition of the /-l-/ medial, which can combine with the above-mentioned medials.
At the other end of the scale, the Kartvelian languages of Georgia are drastically more permissive of consonant clustering. Clusters in Georgian of four, five or six consonants are not unusual—for instance, /brtʼqʼɛli/ (flat), /mt͡sʼvrtnɛli/ (trainer) and /prt͡skvna/ (peeling)—and if grammatical affixes are used, it allows an eight-consonant cluster: /ɡvbrdɣvnis/ (he's plucking us). Consonants cannot appear as syllable nuclei in Georgian, so this syllable is analysed as CCCCCCCCVC. Some Slavic languages such as Slovak may manifest formidable numbers of consecutive consonants, such as in the words štvrť /ʃtvr̩tʲ/, zmrzlina /zmr̩zlɪna/, and žblnknutie /ʒbl̩ŋknutje/, but the liquid consonants /r/ and /l/ can form syllable nuclei in Slovak, and behave phonologically as vowels in this case. Slovak does, however, exhibit true clusters such as in vzhľadom . Another example is the Serbo-Croatian word opskrbljivanje /ɔpskr̩bʎiʋaɲɛ/, though note that ⟨lj⟩ and ⟨nj⟩ here are digraphs representing single consonants: and, respectively. Some Salishan languages exhibit long words with no vowels at all, such as the Nuxálk word /xɬpʼχʷɬtʰɬpʰɬːskʷʰt͡sʼ/: he had in his possession a bunchberry plant. It is extremely difficult to accurately classify which of these consonants may be acting as the syllable nucleus, and these languages challenge classical notions of exactly what constitutes a syllable.
There has been a trend to reduce and simplify consonant clusters in East Asian languages, such as Chinese and Vietnamese. Old Chinese was known to contain additionally medials such as /r/ and/or /l/, which yielded retroflexion in Middle Chinese and today's Mandarin Chinese. The word 江, read as jiang in Mandarin and kong in Cantonese, was most likely klong or krung. Additionally, initial clusters such as "tk" and "sn" were analysed in recent reconstructions of Old Chinese, and some were developed as patalalised sibilants. Another element of consonant clusters in Old Chinese were analysed in coda and post-coda position. Some "departing tone" syllables have cognates in the "entering tone" syllables, which feature a -p, -t, -k in Middle Chinese and Southern Chinese varieties. The departing tone was analysed to feature a post-coda sibilant, "s". Clusters of -ps, -ts, -ks, were then formed at the end of syllables. These clusters eventually collapsed into "-ts" or "-s", before disappearing altogether, leaving elements of diphthongisation in more modern varieties. Old Vietnamese also had a rich inventory initial clusters, but these were slowly merged with plain initials during Middle Vietnamese, and some have developed into the palatal nasal.
Read more about this topic: Consonant Cluster