How can I make Vim recognise ordinal numbers (1st, 2nd) as valid spellings?

Question

If I set spell, Vim seems to only recognise some ordinal numbers: 1st, 2nd, etc. are fine, but anything from 10th to 20th is apparently misspelled. Then 21st, 22nd and 23rd are fine, but then they're all misspellings until 31st...

I'm using Vim 8.1.290.

Why is Vim so inconsistent here, and how can I fix it (ideally without adding th to my spellfile)?

Answer 1

This is an aspell problem; not a vim problem. aspell itself has these deficiencies. You need simply to add the missing ordinal numbers to the dictionary.

$ echo "1st 21st 31st 5th 25th 35th" | aspell -a
@(#) International Ispell Version 3.1.20 (but really Aspell 0.60.7-20110707)
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& th 50 15: Th, Thu, the, tho, thy, THC, Rh, HT, ht, H, T, h, t, nth, Ch, OH, TA, Ta, Te, Ti, Tu, Ty, ah, ch, eh, oh, pH, sh, ta, ti, to, uh, DH, NH, TB, TD, TM, TN, TV, TX, Tb, Tc, Tl, Tm, tb, tn, tr, ts, Th's, T's
& th 50 20: Th, Thu, the, tho, thy, THC, Rh, HT, ht, H, T, h, t, nth, Ch, OH, TA, Ta, Te, Ti, Tu, Ty, ah, ch, eh, oh, pH, sh, ta, ti, to, uh, DH, NH, TB, TD, TM, TN, TV, TX, Tb, Tc, Tl, Tm, tb, tn, tr, ts, Th's, T's
& th 50 25: Th, Thu, the, tho, thy, THC, Rh, HT, ht, H, T, h, t, nth, Ch, OH, TA, Ta, Te, Ti, Tu, Ty, ah, ch, eh, oh, pH, sh, ta, ti, to, uh, DH, NH, TB, TD, TM, TN, TV, TX, Tb, Tc, Tl, Tm, tb, tn, tr, ts, Th's, T's