subset.py: latin-ext missing Latin characters in IPA, Combining diacritics about googlefontdirectory HOT 2 OPEN

Perhaps it needs a full-on "Africa languages alphabet" subset?

Sure, that's a valid subset. However IPA characters are also used
outisde of IPA and African orthographies.
For example, the letter schwa (ə U+0259 in IPA Extensions, Ə U+018F in
Latin Extended-B) is used in Azeri (spoken in Azerbaijan and Iran), or
the letter ezh (ʒ U+0292 in IPA Extensions, Ʒ U+01B7 in Latin
Extended-B) is used in Sami languages (spoken in Nordic countries and
Russia). Both are in MES-2.

It would actually make more sense to have latin-ext complete with all
Latin characters and diacritics, at least those used in language
orthographies. Having a European language subset (or renaming
latin-ext to match it's intended use) would be more appropriate, and
could be similar to MES, along the Vietnamese and African subsets.

There are other possible regional subsets like American, Asian
(including Vietnamese, pinyin), Australasian, or by use (much more
limited) like transliteration (Latin Extended Additional is full of
those), phonetic transcriptions (IPA, UPA, APA), or historical. There
are many ways to organize subsets, but regional zones is probably the
most practical.