There was an article published with a diagram showing Lexical Difference: http://elms.wordpress.com/2008/03/04/lexical-distance-among-languages-of-europe/.
It cites a Russian source "K. Tyshchenko (1999), Metatheory of Linguistics." I can 't find the source. What I would really would like to know is how "lexical difference" is determined.
Another source http://www.ethnologue.com/language/eng says english is "Lexical similarity: 60% with German, 27% with French, 24% with Russian." However, how is this calculated?
The reason I would like to know this is I am attempting to write a program using Natural Language Processing (NLP) to compare languages to English. There are a lot of considerations when comparing two different languages: similarity of words, frequency of use, structure of language, ... the list goes on. A lot of these metrics can be determined using widely available models; however, what I do not know, what metrics matter in regards to understanding what languages have similar cultural backgrounds? I am open to other research as well as opinions on what matters when comparing two languages.
 "Lexical similarity. The percentage of lexical similarity between two linguistic varieties is determined by comparing a set of standardized wordlists and counting those forms that show similarity in both form and meaning. Percentages higher than 85% usually indicate a speech variant that is likely a dialect of the language with which it is being compared. Unlike intelligibility, lexical similarity is bidirectional or reciprocal." ref http://www.ethnologue.com/about/language-info#Dialects