If this is defined, it is not an accepted definition.
Some author in some terrible splatbook may have decided to fill some pages by providing a guide as to how there's a 'language of magic' and how it sounds or whatever but that is in no way an accepted fact actually used in gaming groups that I have ever seen, anywhere, at any time.
People generally leave what magic sounds like up to the imagination of the individual. Sometimes players or GMs will chant some arcane words in-character to indicate spellcasting. This is sometimes drawn from existing real-world languages like latin, greek, or old russian. Sometimes it is ad-libbed. This occurs in a similar fashion to GMs or players roleplaying languages other players don't speak like Goblin or Orcish or whatever, but slightly less frequently. Often, such roleplaying is considered a hallmark of a 'good GM' or 'good group'.
In general, DnD is a storytelling game about making up details of situations that you are not physically present in. A creative, imagination game. Making up details like 'what does magic sound like' is part of the game and in many cases (and most groups) making up details about things that already have details embedded in the crusty depths of some rulebook is perfectly acceptable - either because searching for it for an hour is not considered fun, the details being made up are serviceable for the purposes of continuing the story, or they are having fun making up details as part of an imagination game where that is indeed a large part of the appeal.
There's some further inaccuracies in your question - Perception covers all five senses and distance penalties apply to hearing, smelling, even technically touching and tasting. Needing to be able to see something does not mean it is purely and only visual by any english reading of the term etc etc. Very few groups will take lines like that as hard rules and will usually do something like substitute (either explicitly or implicitly) something like 'perceive' for 'see' in that kind of sentence the very instant someone asks what check to make to identify a spell they can hear (but not see) a cultist chanting the words of.
Likewise I am unsure where you are getting that somatic, material or other components use in the creation of magic is better defined than verbal. Perhaps some crusty sourcebook has all the hand gestures magic requires listed somewhere? If so, i'd expect to see a source. The core rulebook just says that verbal components are an 'incantation', somatic components are 'precise gestures', material components are 'annihilated' in casting the spell etc. How exactly this happens has been described wildly differently - in groups where it's gone into at all that is, and not just 'I cast Sleep'. Not to mention there are descriptions in fluff text in rulebooks (and spell descriptions) that don't follow any specific rules as to how these form - witches that cast spells by dancing or inquisitors that denounce people as a verbal component and so on.
Overall I have seen very little indication of any kind that any of these terms have accepted or expected forms in any gaming group or even printed product. It seems wildly variable from person to person what they consider these terms to mean in practice, and only very few people have ever seemed to even think there should be a single definition for them.
