I use Ubuntu in French and I find the translations to be in a pretty good shape. When I get an error message then I just use the command line to launch the same program in English: LC_ALL=en_US program. Works pretty well.

Recently I switched my parents to a Romanian version of Ubuntu and I was pretty disappointed with the state of translations. Bad wording, inconsistent translations, partial translations etc. But English is not an option for my parents. For now I try to identify translation problems and contribute patches to fix them.