When the value of a country's currency goes up compared to another country's currency that is considered a?

First of all - your punctuation. You need a comma after the second "currency" so as not to confuse whether 'value' or 'currency' is the point - "When the value of a country's currency goes up compared to Another Country's currency, that is considered a...?"

Bad thing, as the cost of goods and services of 'Currency A' go up when compared to 'Currency B.' People will want things priced in Currency B, perceiving them cheaper than Currency A goods and services.