"Your [singing] voice is lovely."
歌声がすごく綺麗ですよ。
Utagoe ga sugoku kirei desu yo.*
This is a strong compliment, rather than a casual remark. I assume you are looking to offer a bit of harmless flattery, so I would probably say it like this. Saying "ne" instead of or after "yo" will soften it a little, and be more like: "Hey, your voice is really nice." His response would be more like: "Aww, pshaw." Saying only "yo" will evoke more of a "thank you" response.
*Note: If you mean his speaking voice is nice, say 「声がすごく綺麗ですよ」 "Koe ga sugoku kirei desu yo."
"I'm nervous."
ドキドキしてますよね。
Dokidoki shite'masu yo ne.
Literally "My heart is pounding". Still, a casual remark. Adding to "yo ne" softens the sentence, so it sounds less blunt. However, I think saying just "Dokidoki shite'masu" (without the "yo ne") would push some kind of conversation out of him, despite sounding more blunt and a little awkward. If you add the "yo ne", he might just smile and say "Mmm."
"I think you're attractive."
ＸＸさん、素敵な人だと思います。
XX-san, suteki na hito da to omoimasu.
*Literally "I think you are a [suteki] person". Adding "person" makes it a little less direct. This is tricky, because it is a very, very forward thing to say, paricularly in Japan. "Suteki" means "attractive," "pretty," "lovely," but also "great," "wonderful", or even "cool". It's something of a vague term (which is good here), unless you specifically say "Your face is [suteki]" or something. However, in context, I'm sure he will understand that you mean he is attractive. You generally wouldn't say words like "suteki", "kakkoii", "kirei" when speaking directly to someone you're on formal terms with. "Suteki" is relatively safe, although I think it might be better to compliment his personality with words like "erai" ("great") or "subarashii" ("wonderful").
"I work as an English-Spanish translator."
私は、英西訳者の仕事をしてます。
Watashi wa, eisei yakusha no shigoto wo shite'masu.
Literally "I am doing the work of an English-Spanish translator." This is relatively simple. The only word that may be confusing is "eisei", because it is probably not that common in Japan. It comes from the characters used in association with "English" and "Spanish". In Japan, to talk about Japan-US relations, or Sino-Japanese characters, you need to create a word using country-kanji. (Japan-US = 日米 "nichibei"; Sino-Japanese = 日中 "Nicchuu"). Because "Eisei" does not involve Japan, it is probably less common there. But if you need to clarify yourself, you can say:
英語とスペイン語の訳者の仕事をしてます
Eigo to supeingo no yakusha no shigoto wo shite'masu.
*Literally "I am doing the work of a translator of the English language and the Spanish language."
Ohaiyo everybody!