This was cleaned up in the Belgian variant of French: https://en.wikipedia.org/wiki/Belgian_French.

- 70 = septante (versus soixante-dix, which is 60-10)

- 80 = huitante (versus quatre-vingt, which is 40-20), *EDIT*: wrong, see below.

- 90 = nonante (versus quatre-vingt-dix, which is 40-20-10)

The article also mentions something interesting I didn't know:

> The use of septante for "seventy" and nonante for "ninety", in contrast to Standard French soixante-dix (literally "sixty-ten") and quatre-vingt-dix'("four-twenty-ten"). Those former words occur also in Swiss French. Unlike the Swiss, however, Belgians never use huitante for quatre-vingts ("four twenties"), with the use of octante in the local Brussels dialect as being the only exception. Although they are considered Belgian and Swiss words, septante and nonante were common in France until around the 16th century, when the newer forms began to dominate.[4]

*EDIT*: This doesn't appear to be true, Belgian French speakers also say quatre-vingt for 80.