Many languages lack a v/w distinction, including Mandarin, all Indian languages, and (sort of) German. Thus, clearly only one of these should be included! Some languages, like Spanish, also lack a b/v distinction. These two constraints together lead us to include [b] and [w], but not [v].
- contrast [f] and [pʰ]: English and Mandarin
- lack [pʰ]: Spanish, Arabic, Greek, and Portuguese
- lack [f]: Philippine languages, Javanese, Sundanese, Blinese, "Native" Indian languages
- lack [f] but have [v]: vi
- weird about [f]; use [ɸ]: Japanese, Korean, Finnish
Summary: omit
- [h]:/[ɦ] English, Indonesian, Hindi, Swahili, Tagalog, Hausa, Japanese, Turkish, Vietnamese, Korean
- [x~χ]: Chinese, Spanish, Portuguese (), Russian
- [h] and [x~χ]: Arabic, German, Scots, Urdu
- as allophone: Tamil
- no [h]: French
French lacks this phoneme, and Spanish+Portuguese are likely to not pronounce because of orthographic confusion. Furthermore, this sound is weak and often goes away.
Weak reject.
Languages lacking a z/s distinction: Spanish, All Chinese, Bengali, Yoruba, Tagalog, Korean (?), Thai, Fulfulde, German. Clear reject.
Note: considering ʂ and ʃ the same for now.
- Missing ʃ: Southern Chinese (e.g. Wu), Korean, Thai, many Spanish varieties, some Hindi varieties.
- No contrast with tʃ: French
English, Mandarin, Hindi, Bengali, Indonesian, Japanese, Nigerian Pidgin, and Turkish have this distinction. Tagalog does too, though [tʃ] "may be pronounced [ts] (or [tj] if spelled ⟨ty⟩), especially by speakers in rural areas. "
Arabic lacks [tʃ]. Most Spanish varieties lack [dʒ], or when they do have it, don't contrast it with [j]; similarly, most Slavic languages have [tʃ] (well, [t͡ɕ]) but lacks [dʒ]. French and Portuguese lack both, collapsing them to [ʃ]/[ʒ], though African French varieties may have them. Vietnamese seems to lack [dʒ].
Conclusion: keep [tʃ] but not [dʒ], for ease on Spanish, Arabic, and Slavic speakers.
Most languages have rhotics. However, they are frequently very different from each other. Consider the "strong rhotics" /ɹ/, /r/, /ʁ/, /ʐ/, and /ɻ/, from English, Spanish, French, Mandarin, and Tamil. Each one of these sounds is exceedingly difficult for speakers of any of the other four to make. Therefore, including any of them in the language would be unwise; and allowing for all would be chaos.
On the other hand, the "weak rhotic" /ɾ/ is a much easier sound to deal with. English, Mandarin, and French lack it, and Japanese does not contrast it with /l/, but Spanish, Portuguese, Arabic, Turkish, and all Indian languages have it (sometimes in free variation with /r/). English even has the sound as an allophone of /t/, and it is not a hard sound to master. Nonetheless, it will be an accent-marking phoneme, at least for English, Mandarin, French, and Japanese, who will tend to realize it as their strong rhotic. There is a strong argument for including it (also because rhotics are great), but for the purpose of reducing accent marking, maybe best to exclude.