As with the case on many words in Mandarin, 妥善 and 妥当 both mean "appropriate" or "proper" in English.
However, what is the difference between these two words, and how can I use it properly?
Both '妥善' and '妥当' means "appropriate" or "proper" .
There are minor difference:
'妥善' implies "(satisfactorily) appropriate"
'妥当' implies "(correctly) appropriate"
對員工遣散有妥善安排 = There is a proper arrangement for severance. (everyone should be satisfied)
對員工遣散有妥当安排 = There is a proper arrangement for severance. (everything by the book without mistake)
妥善地佈防 = properly set up defensive positions (satisfactory on all accounts)
妥当地佈防 = properly set up defensive positions (follow all protocols correctly)
If someone said he will give you a 妥善的補償, he is trying to assure you that the compensation will be fair and satisfactory; If he said he will give you a 妥当的補償, it means you will get whatever you are entitled to. No more, no less.