There actually aren’t too many of these. While there are a lot of minor island dialects, the people of the isles tend to be long-lived, and there aren’t all that many of them – so the number of major languages is relatively limited. Just as importantly, the number of other dimensions that can be reached from the isles is relatively limited – and the number which have any regular contact with the isles is even more limited.
There may once have been many more languages out there – certainly there are strong indications that the Shadow Elf and Veltine founders spoke many languages – but there isn’t enough left of any of them to reconstruct, much less speak.
These days, there are only three minor languages of any real importance:
Dosutine: Dosut is one of the most easily reached of the nearby dimensions – a chaotic realm of floating patches of land, a dangerously localized set of environments, powerful spellcasters, and their bizarre minions. Many of those minions can be summoned and bound to service due to the restraints laid on them by their masters at home (although this risks attracting the notice of said masters), hence the study of Dosutine is popular with summoners – especially since the tongue is understood by the inhabitants of several more distant (if equally chaotic) planes. The language itself is difficult for “normal” humanoids to pronounce, but has a strong gestural component, and (with a success check) can be used to cast spells that normally require verbal components silently – although this adds a gestural component which is incompatible with any normally-required gestural components. It’s written form consists of a complex sequence of subtly-different curving lines.
Krellian Glyph-Spirals: Bizarrely by most standards Krellian has a written form, but no spoken one. Each full thought is written as a spiral of impression-glyphs, with positive or negative emphasis shown by direction of the spiral. The writing technique consists of carefully composing and organizing the thought, envisioning the structure of the glyph-spiral – and then spending one or more points of Power to imprint it on a surface. (Those with an appropriate speciality may imprint glyph-spirals on the structure of space itself, leaving them hanging in the air). While this takes at least as much time as conventional writing, it requires no implements other than Power. Psionically-empowered glyph-spirals can be used to either imprint or erase patterns on the mind – which makes anyone known for their use generally suspect, at least to non-psychics. Learning to read Krellian is often the first step in developing psychic powers.
Shu: A tongue primarily known from ancient manuscripts, Shu is built upon harmony and balance, to the point where it has difficulty handling definite statements or unbalanced concepts. While complex, tonal, and slow – if beautiful – in conversation, Shu is uniquely suited to recording the combination of physical, mental, and spiritual balances which go into the mystical martial arts. A martial art recorded is Shu can be easily learned without an instructor – and, if two speakers of Shu with a link speciality are in telepathic contact, one can guide the other through the use of any physical skill without penalty.