Usage patterns
〈事〉が達者to be proficient at (a skill, language, etc.)
He is proficient in English.
足腰が達者to have strong, healthy legs and hips (esp. of the elderly)
My grandmother is still spry on her feet even at eighty.
お達者でtake care; stay healthy (parting well-wish, esp. to the elderly)
Please take good care of yourself and stay well.