What about "bear up" or "cheer up"? Or "keep your spirits high?" But why don't you supply us with a little bit of context? Would you be talking to someone who has lost a dear one? In that case my expressions wouldn't be suitable, I guess
I mean if somebody have difficulties........at work for example.
Maybe this person feel frustrated and do no react against the matter.
I would like to say him, do not feel depressed but at the contrary that he has to front the situation with....strengh? with....energy? with...a sort of anger?
I would be very pleased if somebody may help me with german too.