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Other than Latin, are there any languages that have a word for the number 18 that means twenty minus two?
A quick glance at some of the numeral systems of languages in the Indo-European reveal that 20 - 1 is common and there are some 30 - 1 words.
But I only know of 20 - 2 in Latin (duodeviginti).
There is a paper that gives an overview of the additive, subtractive and multiplicative derivations of number-words as used in the three dialects of Yoruba.
I'll quote a few things here, but the number system is far too complicated, and needs the paper I linked to to describe it.
In the first pattern, it uses addition solely to derive the number words but with a counting pattern where 'ten', 'twenty' and the added number units are taken as a whole. In the second counting pattern, subtraction is used to derive number words but this is applicable only to three numbers i. e. seventeen – /mɛ́ɛtadínóɡu/, eighteen – /méèʤìdínóɡu/ and nineteen – /mɔkɔdínóɡ́u/.
In addition
Most importantly, the idea expressed in [Standard Yoruba] and [Yoruba Ifè Nigeria] ... is 1 + 10, 2 + 10, 3 + 10, 4 + 10 for eleven to fourteen; and 20 - 5, 20 - 4, 20 - 3, 20 - 2, 20 - 1 for fifteen to nineteen; twenty (ogún) is a basic word.
The paper also compares the preferences of the older and newer generations of people when it comes to specific numbers.
The Salishan languages Bella Coola (Nuxálk) [Denzer-King, pre-publication[PDF] and 2009[PDF]] has "subtractive counting" for 3, 8 and 9:
1 smaw
2 ɬnus
3 ʔa-smús ‘being next to + 4’
4 smús
...
8 kʼi-ɬnus ‘lacking or without 2’
9 kʼi-smaw ‘lacking or without 1’
10 cʼklakt
Some sources give 18 as not subtractive, but others have 18 as subtractive:
18 smawlakt-nus ‘11+7’
18 cʼklakt puƛʼs ʔa kʼiɬnus ‘10+lacking 2’
Ainu is one of those: (http://www.sf.airnet.ne.jp/ts/language/number/ainu.html)
1 sinep 1 obj.
2 tup 2 obj.
3 rep 3 obj.
4 inep 4 obj.
5 asiknep 5 obj.
6 iwanpe 6 obj.
7 arwanpe 7 obj.
8 tupesanpe 2 obj. to 10* obj.
9 sinepesanpe 1 obj. to 10* obj.
10 wanpe 10 obj.
I don't know any off the top of my head, but Eugene S. L. Chan has a large number of languages for which he has collected basic numeral terms:
