To reproduce: 1) Create a collection in pt-BR only; 2) Visit amo and set en-US; 3) Try to manage your collection. 4) Try to only edit the pt-BR field, and submit;... It forced me to add an en-US translation to my collection. So I just ignored the little, and new forced en-US tab, but when I submitted my changes ( only to pt-BR ) it generated an error blocking the actual update.
Thanks for filing this. In an effort to not drown in existing reports we're aggressively closing old enhancements and bugs to get the buglist to a reasonable level so we can scope and process bug sprints in an effective manner. Patches for this bug are still welcome.