I never ever considered PokeSpeak is a form of "language". More correctly speaking, it is not any syntactically translatable language in terms of linguistics in the sense of those languages developed and spoken by human beings, where there exist a methodical system in grammatical structure and vocabulary construction, such that every educated individual can learn to speak that language from ground zero. PokeSpeak, from my POV, they are nothing different from the meowing of a cat and barking of a dog or tweeting of a bird or neighing of a horse. That is just a sound they make when they want to express their emotion, where that is conveyed through the tone and mood of the voice, but not through the word itself.
That's why personally, I always waver unfavorably whenever I saw writer write out PokeSpeak as like a form of human language, quoting them with quotation marks or whatever parenthesis. Bonus point if directly writing the sound itself out instead of translating them. These are some examples on the top of my list:
1) "Pika, pikapikachuuuu--!!!" The electric rat was unsettling, pointing to the shrub nearby. It seems like something is hiding.
2) "Pi~ka~? <What's the matter?>"
3) "Hey Pikachu, did you manage to talk to Charmander?"
"Pi! Pika, pikapi,pikapikapikachu~"
"Ah...... So are you trying to say it sit still at there waiting for the sun to rise and shine?"
4) "<I'll be the one to win this match. Now, are you prepare to be the coal of my fire?>" Charizard howl towards its opponent aggressively, determinedly ready for the upcoming battle that will be start just within the next few seconds.
A linguistically comprehensible language, or simply any languages spoken by human being, the meaning of speech is conveyed largely through the choice of words itself, and the meaning is refined and stylized through grammar. Tone and mood of voice may also be one factor in conveying the meaning of speech, but in writing, because we cannot read the tone and mood by simply looking at the texts (unless you uses interjection, but interjection itself is yet not any lexical words with concrete meaning), hence vocabulary and writing style become the crucial factors.
And that is exactly what PokeSpeak failed as a language, because it doesn't have vocabulary. They are at best functioned as interjection in part of speech. So even one write out what the pokemon "spoke" in its original voice, no reader can comprehend what the hell does "Pi! Pika, pikapi,pikapikapikachu~" means, so it just becomes rubbish texts.
And that's why, I personally preferred to rather narrate what the pokemon trying to convey through expositions. Not only does that seems less awkward from writing POV, but it also established a perception concept to the reader about the writer hence myself, which is I see pokemon is not the same as human being, hence I do not treat them the same as human being, and I don't let the pokemon characters within my fic act too much like human being, including communicating with one another through talking.
(BTW, interesting Real-Life fact: Only human being communicate with one another through the means of linguistic language, either verbal or written. But animals and insects and plants, 99% communicate with one another through non-verbal means)