Take the Indo-European family of languages. They arose in a broad arc of the globe from Iceland, across Europe (including English) through to northern India. This vast family is believed to have its origins in the Caspian Sea area several thousand years ago and spread through migration and contact to Europe and India and splintered into many of the world's major languages. This website easily shows this 'genetic' link by listing numbers 1-10. A few examples:
English: one, two, three, four, five, six, seven, eight, nine, ten
Welsh: un, dau, tri, pedwar, pump, chwech, saith, wyth, naw, deg
Russian: odín, dva, tri, chety're, pyat', shest', sem', vósem', dévyat', désyat'
Bengali: æk, dui, tin, car, pãc, choy, sat, at, noy, dosh
The notes on the site throw up some interesting insights into other languages:
- Numbers in Yoruba (Africa) are built on substraction, so 46 is sixty-less-ten-less-four.
- In Kumbundu (Africa) the number 7 is a euphemism: to say 7 directly is taboo, so they use a word derived from '6+2' (I guess this is no more weird than numbering the 13th house 12A, or talking about the 'Scottish play').
- Yumbri (Thailand) claims to have no numbers, only little and much.
- There are a few base 5 systems, but there are some that are base 4 (so 7 is '4 and 3'), base 8 and binary.
And if the existing 5000 languages are not enough, there is also a slightly nerdy section on imaginary and sci-fi languages, as well as a bewilderingly optimistic array of artificial languages.
Strangely sign languages are omitted. Although they all (as far as I know) use the fingers for counting, each sign language has different ways of doing it. British Sign Language numbers and American SL numbers have only 1, 2, 4 and 5 in common:
Interestingly, BSL for eleven and twelve are (like English and French) irregular, i.e. they don't follow the pattern for the rest of the teens.
Link for Numbers in 5000 Languages http://www.zompist.com/numbers.shtml