I remember posting the same thing once upon a time, but since then I've had many messages saying my suggested translation is now accepted. It takes some time, and there are a lot of changes still to be made, but things are getting better.
'Trousers' is the British word and 'pants' the American. Both should be allowed. We do not always say 'pair of' as just saying 'trousers' is sufficient. It can sound pedantic to say 'pair of trousers' in an informal conversation.
When the Duolingo team gets further along they may include Traditional Chinese and Traditional English. But for now the lessons seem to only be in Simplified Chinese and Simplified English... (coming from a native speaker of 'Merican!) ;)