Launching sites without usability testing and 508 testing is a waste of time and money - it's always more expensive to fix these issues when left to the last minute. Rather, institutionalizing user testing (like GSA's First Fridays, for example) as well as 508 testing into the development cycle of government websites will result in better, more efficient and cheaper products .
Test multilingual content / design with representative users to ensure usability and understand audience needs.
Timing is everything. Doing user research (usability testing) after the redesign is too late in the process. Find what your target audience needs by conducting user interviews early in the project. Avoid learning what you have done wrong by the time is too late to fix it.