Last night, we started playing Ruins of Azlant and quickly ran into what will inevitably be a key communication issue for the duration of the campaign:
Can humanoid races speak Aquan clearly and be understood underwater?
Clearly, if a creature has the aquatic type, it's a non-issue; of course they can speak Aquan underwater clearly. So water elementals, merfolk, faceless stalkers, and aboleths all speaking the same language works.
The thing is, water elementals, merfolk, faceless stalkers, and aboleths don't have anything like the same biology, so it's hard to make the case that there is something special to their form that enables clear and intelligible underwater speech. Their varied biologies suggest that the intelligibility of Aquan underwater is a property of the language itself, not a feature of the subtype of the creatures speaking it. That said, it's fantasy and real world biology in Pathfinder is slippery slope toward fun killing.
I thought for a second that it might be more about those creatures' ability to breathe underwater, inherent to all creatures with the aquatic subtype. The thing is, that ability does not determine whether a character can speak underwater.
From Aquatic Adventures:
"While various spells have different effects underwater, the most fundamental hindrance to spellcasting, at least at low levels, is the fact that a creature holding its breath must succeed at a concentration check (DC = 15 + spell level) to cast a spell at all, whether or not the spell has a verbal component. If the spell has a verbal component, expelling the air needed to incant the spell reduces the creature’s remaining number of rounds of breath by 3 (which stacks with the reduction from performing a standard or full-round action; see the Drowning section of Underwater Hazards and Features on page 47), and a creature can’t fnish the spell if it doesn’t have enough breath left. Spells that have verbal components and casting times of swift or immediate actions instead decrease the caster’s remaining number of rounds of breath by 1."
So a PC can speak clearly enough to cast spells underwater. And there is no biological limitation on a character's ability to speak Aquan. Aquan is the language that aquatic creatures use to communicate underwater, so much so that it is the ONLY language spoken by water elementals. Therefore, I ruled that speech in Aquan was free underwater, and by its very nature could be clearly heard and understood. I plan to charge rounds of breath (as per the spellcasting/bardic performance rules) if PCs get too chatty, but this is the only ruling that made sense to me.
For balance reasons (and real world sense), though, I think it makes sense that humans shouldn't be able to speak any language clearly or to make out clear speech underwater without the ability to breathe water.
I told my players I may retcon my decision, and I was wondering what the boards think.
I think your interpretation of the quoted rules is correct. When i was taking swimming for a PE credit in highschool some of my classmates and I discovered that you could safely yell at each other underwater. The main issues were, you would have to surface for air a lot sooner, you had a ton of bubbles in front of your face while you talked and you had to yell to be understood clearly since your voice was heavily muffled.
So, I think the rules are fairly on point for a fantasy setting were fun > realism.
One thought that comes to me though if you want to adjust the aquan language. Maybe it's really hard to understand someone who is speaking the language when they aren't underwater and it's very clear when they are. You could even rule that peaking aquan doesn't reduce the amount of breath you have left, as a result of how the language is spoken.
Thanks for your thoughts and advice, everyone.
With Air Bubble up, or Water Breathing in effect, I would say using Aquan is free and without issue. Otherwise you have the run-out-of-air issues already addressed.
/cevah