i18n, c14n, and L10n are all just ways of abbreviating fairly long words that often get mentioned (and thus typed!) a lot. the 18/14/10 stand for the number of characters omitted from the word:
- internationalization = i + 18 more characters + n
et cetera.
The others, like "log4j" are more just using common abbreviation techniques in computer text/slogans, like using "2" instead of "to" or "4" instead of "for".
Because the abbreviations are mostly just things that became accepted over time, there's not necessarily an authoritative source for them, but you'll often find them mentioned on things like Wikipedia pages on certain topics.