Technically, we're all perverts here.
Nutaku's translator might be a choice for you, which is Google.
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What's harder? Latin or Japanese?
Japanese cause their writing system is plain dumb and inefficient.
The langauge itself? no clue though.
As far as the language itself? Probably latin. Japanese itself isn't hard to learn at all.
Reading it is a whole different story, however. There is what? 50 000? 85 000 kanji characters? Although you only need a fraction of that in order to read something as simple as a porn game, we're still talking about memorizing thousands of characters before you can somewhat read it.