From a purely legal standpoint, yes it is copyright infringement. But if you insinuate fan translation cost the japanese writers/developers money, you're wrong.
Fan translations are usually happen for Anime/Manga/Games, that don't leave the japanese market. That means: the japanese company always calculated only with the japanese customers to bring in the money and also see it as a risk too big financially to support other markets. Fan translations pose no risk for them, as people do it for free in their spare time.
There is another effect: fan translation create a fan-base in other countries so they decrease the risk for the publisher to later translate sequels or other stuff themself. So probably the japanese publishers even win money in the long term, as fansubs create a market without a financial risk for the publisher.
At last another example. The brasilian author Paulo Coelho put fan translations of his novels to his website if the language wasn't covered by official publishers. That in the end made him an international successful author, as these fan-translations did create a market for his books in different languages.







