Language Point 19

Learning a foreign language has been a most trying experience for me, but one that I wouldn't trade for anything. (Para. 8)

Meaning: Learning a foreign language has been an experience full of difficulties, but I wouldn't exchange it for anything else.
trade (in) ... for... : exchange ... for...
He decided to trade his car for a truck. 他决定用小汽车换卡车。
In order to pay off his debts, he had to trade in his piano for money. 为了还债，他只好把钢琴拿去换钱。
Cf. trade on: make use of
He traded on his brother's kindness to get more money from him. 他利用哥哥的善良，想从他那儿多弄点钱。
The senator's son traded on his father's name when he ran for mayor. 参议员的儿子在竞选市长时利用了他父亲的名望。