The modern tongue of the sliths, spoken in the homeland of the sliths in the time of the assassination of Hawthorne and the Empire War, has undergone several sound changes since the classical period. Fortunately, it remains quite regular, if at times somewhat complicated.
The vowels have, in fact, undergone the most dramatic shift since the classical era. Early in the Modern Slith period, some long vowels and short vowels began to develop qualitative differences in addition to their quantitative differences. Late in the period, the quantitative differences disappeared entirely, leaving only qualitative differences.
Late in the classical period, pronunciation lost the close front rounded vowel (U). Short u was unrounded to i. In most contexts, long ū was by analogy shortened to short u and then unrounded to i. In certain contexts, the shortening did not take place, and the long ū shifted directly to long ō.
Also, in certain contexts, a new U vowel was introduced with a completely different quality than the old U had.
As noted above, orthographical convention changed after the classical era: since the long/short distinctions changed to qualitative rather than quantitative, the significant distinctions were marked with an H, instead of a doubling or a macron. This became possible because post-vocalic h was frequently dropped, with compensatory vowel lengthening, and the ones that weren't dropped were shifted to other sounds (most frequently kh).
Also, unlike in the classical tongue, semi-vowels i and u did assume their consonantal qualities in the modern tongue whenever followed by a vowel. That is, i was pronounced the same way as the y in English you, and u was pronounced the same way as the w in English we.
A great many vowels underwent shifts in a great many positions, but most notable was that many diphthongs were simplified.
All stops are aspirated. The stops, by and large, did not change, except that long stops were shortened to the same sounds as short stops, and several stops were shifted to fricatives.
The liquids and nasals underwent the most significant changes among the consonants from the classical tongue to the modern.
Both trills, r and rh, shifted to approximants. The uvular rh became a uvular approximant, which very quickly became indistinguishable from the uvular fricative gh, and the spellings were simplified to simply gh for both. The alveolar r remained distinct as an alveolar approximant, but in some dialects today it is being realized in syllable codas as simply a lengthening of the preceding vowel, so that classical kor is now often pronounced as if it were classical kō (with the length and quality of the classical long vowel, even though neither match the modern short vowel).
The long rr shifted to a uvular trill, which could have been indicated with the old digraph rh, but this was deemed to conceal the etymology too greatly. Most current-day speakers have undergone another shift, moving the rr to gh, which has caused some less-educated sliths to have trouble spelling some words. Long mm was generally shortened to short m, although in some cases it shifted to n (and vice-versa: some n shifted to m). Long ll shifted to li before a vowel, and otherwise it shortened to l.
In many positions, many fricatives were devoiced, shifting z to s, for example.
Long fricatives generally were retained in modified form. They no longer were held for longer time, but they often sounded harsher and hissier than short consonants. This occasionally led to insertion of stops.
Two short vowels in succession create a diphthong, never two separate syllables. Likewise, consonants are slurred together as much as possible, creating many affricates. Example: ksevoss begins with the same sound as English fox ends with.
Stress became heavier in the modern tongue than it was in the classical. It is still somewhat less intense than English, but it is more forceful than Spanish. Stressed syllables in the modern tongue generally last as long as heavy syllables did in the classical tongue. Also, in trisyllabic or greater words, primary stress alternates with secondary stress, with one unstressed syllable in between stresses.
Stress became largely penultimate (on the second-to-last syllable). Example: Bahssikava is primarly stressed on the second-to-last syllable, and it has a secondary stress on the fourth-to-last (first) syllable.
A few words that had stress on the antepenultimate syllable (the third-to-last) shifted stress, but somewhat more often, antepenultimate stress was marked with an H in the antepenultimate syllable, which also indicated holdover long vowels (and the two almost invariably coincided). Example: Vahnatai has a primary stress on the third-to-last (first) syllable, since it has an H in it, and it has a secondary stress on the last syllable. Long consonants also could indicate irregular stress on the antepenultimate syllable. Example: Thassaka receives a stress on the antepenultimate syllable because of the double S.
Foreign words that had stress in other places than the penultimate or the antepenultimate syllable received secondary stress in their originally stressed syllables and primary stress according to the alternating stress system.
Additionally, a short I can never receive a primary stress, unless there is no preceding syllable, and a consonantal one cannot receive a stress at all. Examples: Slithzerikai is primarly stressed on the third-to-last syllable, because the second-to-last syllable has a short I, and it receives a secondary stress on the last syllable. Ithik, on the other hand, is stressed on the second-to-last syllable, even though it has a short I, because there is no preceding syllable.