What is this? This is a reform on Poplengwo orthography to take into account various criteria more objectively than before.
What's changed? Not much. The r is now preferably pronounced as an approximant ([ɹ], [ɻ]), not as a trill. The phones [h] and [x] are merged as a single phonological category: the letter h. The phones [ʃ] and [ʂ] that were written as c, now take the place of the letter x. The letters c and q are not used. See below the resulting alphabet and the pronunciation of each 24 letters:
a [a]/[ɑ], b [b], d [d], e [e]/[ɛ], f [f]/[ɸ], g [g], h [h]/[x]/[χ], i [i], j [ʐ]/[ʑ]/[ʒ], k [k], l [l]/[ɭ], m [m]/[ɱ], n [n]/[ŋ]/[ɳ], o [o]/[ɔ], p [p], r [ɹ]/[ɻ]/[ɽ]/[ɾ], s [s], t [t], u [u], v [v]/[β], w [w], x [ɕ]/[ʂ]/[ʃ], y [j], z [z].
Here are some criteria that should be taken into account to make the language as simple and consistent as possible for the greatest possible number of people:
It is pronounced as an approximant in English, and in Chinese as a retroflex fricative ([ʐ]) at the beginning of a syllable, or an approximant at the end. As the pronunciation as a retroflex fricative realization would conflict with the pronunciation of j, we don't allow it. Its pronunciation as an approximant is common to both languages, so choose it as the prefered pronunciation. The trill ([r] used in Spanish is not easy for a Chinese or English speaker to produce, what's more it sounds quite different from the approximant, so we don't use it in this reform. However the flap ([ɾ]) also very common in Spanish and Portuguese sounds close enough to the approximant, so Spanish speakers can use it if they are unable to produce the approximant.
It is pronounced [x] in Chinese and [h] in English, which are quite similar sounds, so they can be considered as allophones in Poplengwo. Therefore, we assign to both sounds the letter h.
There are some pairs of phonemes in Chinese that most other languages (English, Spanish...) don't differentiate. These couples are, in pinyin: (q, ch), (x, sh) and (j, zh). These couples therefore have to be merged in Poplengwo phonology.
If we choose to keep similarities with writing in natural languages, then we will prefer to keep the graphemes 〈ch〉 (used in Chinese, English, Spanish...) (or simplify it to just a 〈c〉 because this letter is unused otherwise), 〈sh〉 (used in Chinese, English...) and 〈j〉 (used in Chinese, English...). This leads to a pronunciation ambiguity, as we don't know for sure whether to pronounce the letter h alone or with its preceding letter. This also leads to a writing ambiguity as 〈c(h)〉 could as well be written 〈tsh〉. Finally, the letters q, x are left unused. In the end, with so many issues, this option doesn't seem like a good idea.
If we choose to write all phonemes with monographs, then we have to lose a lot of similarities with the English writing. Instead of using the graphemes 〈ch〉, 〈sh〉 and 〈zh〉, we will use their counterparts in the pinyin couples: 〈q〉, 〈x〉 and 〈j〉 (and maybe even take the 〈c〉 from pinyin to make a [ts] sound). This still leads to a writing ambiguity, as 〈q〉 could also be written 〈tx〉, and 〈j〉 seems to start with a 〈d〉 (and 〈c〉 can obviously be written 〈ts〉).
If we want to avoid all ambiguity of writing, all we have to do then is to discard 〈q〉 and 〈c〉 and that is how we ended up with the present reform. Since not using the letters c and q at all can be seen as a waste, we considered using q for the sound [ŋ]. Indeed although this sound is used a lot in English and Chinese, is doesn't have any unique letter assigned to it. Instead, it is written 〈n〉 before a k or a g, or 〈ng〉 at the end of a word. The problem with this idea is that such an exotic pronunciation of the letter q is not used in any language, so it would seem unnatural to everyone. Therefore we accept this little violation of the one letter per phoneme rule for the sake of similarity to existing natural languages.