jali = whale (season 2 episode 3)
As far as I'm aware, the only word we know from the language is jali, the word for "whale". This is misheard by Jason and Brett as Charley, and they assume it's the name for the individual humpback whale befriended by Neri. But in season 2 episode 3, it's made explicit that "jali" is the generic name for "whale" in her native language and not just the name she's given to this individual. From the transcript (emphasis mine):
Father: The other survivors perished one by one. Until, my daughter – you and I were the only ones left alive on the alien shore. Then, Neri, as a child, you fell from a high place into the sea. A great whale – in our language, a jali – was there to save you when I could not. He returned you to my arms. You were then able to talk to the great jali because, my daughter, you must know that you possess a gift.
Adding background to the name "Charley", at OP's request. The first mention of the name is in season 1 episode 2:
Neri: They look for you. Charley sees them.
In the next episode, the boys at first assume Charley is a human:
Jason: Who is this Charley anyway? Her boyfriend or what?
... but eventually they realise the truth:
Jason: Your best friend is a humpback whale. And he gave you the okay to come here.
In season 3 episode 6, we hear the language spoken on-screen.
From the transcript:
(music) (Speaking foreign language)
Kal: My mother.
Brett: What’s she saying?
Kal: It is the book of the ship. My mother tells every day.
Neri: She says it is day seven of the growing of the summer moon. She says this will be the last day she will speak.
Jason: I get it. It’s like a diary, a log book of the ship.
Kal: Yes, that is my mother’s work.
Neri: She says the ship has trouble. The machines which power and guide it have broken – and they cannot fix. Ship cannot stay in orbit. Earth, which they come to study, is now close… But is impossible to make landing safely. She says ship will crash on earth, on opal planet, will crash soon.
Brett: That’s why she said it was her last entry.
(Speaking foreign language)
Neri: She speaks of her son. She speaks of Kal. She fears not to make it through crash or Kal’s father. They have built special sleep box to put Kal in. She’s asking if anyone lives, they will take Kal from sleep box. She’s saying Kal is fine and strong. Parents’ last thoughts is love for him, hope for him.
Jason: What’s she saying?
Neri: She says there is a task to do, a very important task. She says, “take up the crystal.”
Brett: What does that mean?
Neri: Ship is falling fast. Now there is no hope. They cannot stop. They cannot control!
There appear to be no published resources for this language.
Not much thought went into the words used in that scene in season 3 episode 6, and there was no crafted language. To make sure of this, I emailed Lars, the guy who runs the above-mentioned site for Ocean Girl resources, to ask him about it. He gave me the following response taken directly from a friend of the actress who spoke the language in that scene:
The language was made up by the actress.
Any resemblance to any language is coincidental.It was created especially
for the character.
The character talks about Kal's home planet, it's destruction and his
coming to earth to fufil a mission to find a crystal. That's about all the
information we have.
So that's about it: the best canon-based answer I can give to this question. The Ocean Girl franchise, unlike say Star Trek or Lord of the Rings, is apparently not popular enough for anyone to have bothered creating a fully fledged language for it.
Out of canon
Several fanfictions have been written based on the Ocean Girl series, and some of these go into a little more detail about the language than the show does.
In particular, Judith Kenyon's novelisation of season 2, available on this site, mentions some words of Neri's native tongue in its final chapter, chapter 14. This chapter covers Mera's arrival on her home planet, after the concluding episode 13 of season 2. Note that Mera herself does not speak the language:
Onoelle bowed laughingly to the whole group, and introduced Mera. She spoke for a long few minutes in the other language. Mera heard her name and Neri’s.
A furred creature came up out of the water. It looked like—a panther was Mera’s first thought, but its legs were too short and funny shaped. More like an otter, but definitely catlike when it sat down to lick water from its fur. Mera asked, “Dangerous?”
“Pet.” Rulmyr told her, and said what it was in the ocean planet’s language.
While they walked the ocean children tried to teach Mera their language by pointing at things and saying the words. Salali started it by communicating that her name was also the name of a certain bluish shell. Laeka’s name meant ‘wave’ but there seemed to be several different words for ‘wave,’ for calm waves or stormy waves. Ilona had to draw in wet sand to show that the striped dolphins were called ilonar and her name was the word for one of their babies. Arran took the stick and pantomimed that his name meant spear. He seemed quite proud of it.
The first words Mera learned were, “Come see what I found.” Her friends were always saying that.
Mera answered, clumsily but in the same language, “You climb rocks since very small. I did not!”
So now we have a small collection of words:
- jali = whale
- salali = a certain bluish shell
- laeka = a kind of wave
- ilonar = striped dolphins
- ilona = striped dolphin baby
- arran = spear
However, Judith Kenyon's novelisation is not officially sanctioned by the showrunners, so it's essentially a fanfiction.
This fanfiction also gives us another word:
- shushali = test (a special test ritual on the Ocean Planet)