Hi pegibson,
General Skilled Migration:
For applicants who have turned 18 at the time of application and who are assessed as not having functional English, the second instalment is $4885. For any other applicant, the second installment is nil.http://www.immi.gov.au/fees-charges/_pdf/visa-pricing-table.pdf
You can prove functional English by IELTS score 4.5 or if ur first language is English and have a current passport from the United Kingdom, United States, Canada, New Zealand or the Republic of Ireland
So any applicant (dependent) who is over 18 and didn't provide evidence of functional English , will have to pay the second installment
How to prove functional English is here http://www.immi.gov.au/skills/skillselect/index/functional-english/
Cheers