#i18n
i18n stands for internationalization.
i + 18 letters + n
Take the first letter, count up to the second last and then the last one.
Internationalization describes the process of planning and developing a product (normally software) that can be adapted into different cultures and languages without changing the core architecture of it afterwards.
#L10n
This is localization. Works the same way as #i18n.
Localization is the actual work that needs to be done to make the product support multiple cultures and languages. For example translating a user interface.
#T9n
Again, same principle, but this means translation.
#G11n
The last one of this group. Short for globalization.
Globalization describes the whole life cycle of a global product. This starts with the design and development until marketing and adaption into different markets.
#xl8
Stands for translate.
x = trans
l = l
8 = ate
#xl8r
Similar to #xl8, just instead of translate, it means translator.
x = trans
l = l
8 = ate
r = r
Alternative you could use #t8r, but #xl8r is much wider used. At least according to a google search:
“#xl8r” translation ->About 1,010,000 results
“#t8r” translation -> About 42,400 results
Instead of the short versions, people also use the normal words, but since you have only 140 chars at your disposal, they are not very common:
#localization
#translation
#language
I’ve already made a similar post about this topic a while ago:
http://blog.supertext.ch/2010/04/was-bedeuten-l10n-und-i18n/
And Jennifer McNulty wrote another nice explanation here:
http://blog.adaquest.com/2011/09/23/g11n-i18n-l10n-translation-%E2%80%93-sure-you-know-what-these-mean-or-feeling-gilty-because-you-need-clarification-2/
You have questions about other tags? Check out #tagdef.