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. 他決定用小汽車換卡車。
In order to pay off his debts, he had to trade in his piano for money. 為了還債，他只好把鋼琴拿去換錢。
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，想從他那兒多弄點錢。
The senator's son traded on his father's name when he ran for mayor. 參議員的兒子在競選市長時利用了他父親的名望。