See here: http://en.wikipedia.org/wiki/Common_European_Framework_of_Reference_for_Languages

The IELTS and TOEFL exams are used by universities to assess the English language ability of non native English speaking applicants. IELTS is widely used in the UK and Australia and also recognised by most American and Canadian universities, including he Harvard Business School; TOEFL is used mainly by American universities, though also accepted in the UK and Australia.

In the United States, the TOEFL (Test of English as a Foreign Language) and TOEIC (Test of English for International Communication) are the ones frequently mentioned. TOEFL for college-bound students and TOEIC for business people. TOEFL: http://www.ets.org/toefl/ TOEIC: http://www.ets.org/toeic/ The other international standard I'm familiar with is the JLPT (Japanese Language Proficiency Test), and there are several levels of testing for that. But the certificate they give you for passing each level is pretty cool.

For English (British English) See this group here (italki): http://www.italki.com/groups/3713

For English there is IELTS; for Chinese there is HSK.