Besides its refreshing and positive feel, in the English-speaking world, it can also mean a "defective product" or a "result that's below expectations." So, it can be used wittily when talking about a disappointing experience.

In the West, there's a famous saying: "When life gives you lemons, make lemonade." As such, the lemon emoji can carry the message of overcoming difficult situations positively. So, it symbolizes not just sourness, but also life's bitterness and the wisdom to overcome it.