You can talk however you want. We have orcs that were raised by humans and don't know orcish and only know the way humans speak. There's no law that says you have to speak Orcish (except the one where you aren't allowed to say "hail, king, lord, or sir"). You could talk like a refined Englishman if you really wanted to. But you also have to realize that some orcs will probably make fun of you for talking like a "pretty human." Gragarn thinks English is very flowery and doesn't like to speak it. Orcish is guttural and bold, fitting orcs. He'll speak it if have has to for diplomatic reasons, but I usually throw in some accent even when doing that.