Nabokov was very discouraged when he translated his Lolita into Russian. And he spent half a year on it. So should I try the translation myself?
If you have the time to do so, and there is a want for the translation, I say it wouldn't be a bad idea. By being able to do the first translation yourself you can be sure all the little things that make it through, that way some important piece of characterization doesn't get lost.
Though in the end, it's also about time. If you don't have the time to do the work it might be better to supervise it instead of doing it yourself.
I would always seek help from a professional translator, no matter how proficient I deem myself in the target language. A professional translator has studied the intricacies of both languages (and probably a few more); he has linguistic tools at his disposal I might not even imagine existed; he can look back at years of professional experience; and he is getting paid to get it right, it's his entire job. He will deliver a better result much faster.
Most importantly, though, you can always talk to him. In fact, a professional translator will always be proactive about talking to you should he have any questions. And even if he's totally happy with his output, you can still say, "nope, that's not quite what I had in mind. You've translated the name X as Y where I would have preferred Z, and in this sentence here you are actually implying something that is not true to my original".
Now, I'm not saying that you should never even think of translating any works of yours yourself. If you feel like trying, by all means do. It's a fascinating experience. However, the thing is that if you do the translation yourself, you will still need to show it to a professional editor afterwards, or at the very least have it proofread by a few native speakers of the target language (one is never enough). So you will still have to work together with another person of five, except that it will be much more cumbersome and take forever.
Lastly, even if you invest a few years and achieve true mastery in translation, it will still be a trade-off: never forget that you could be spending all that time writing new works instead.
I think that translation is an art in itself, not unlike writing in that it's also a creative endeavor. If you want to do it because you think you'll get something out of the creative experience, I'd recommend you go for it--with help from a professional translator. But if you just want your work out there, I'd recommend someone who is a translator because they won't be emotionally tied to the work like you are.
I think languages are very different in a lot of subtle things, so I wouldn't trust a third party to translate my thoughts, the way I write, and my subtle hints and intentions into another language I know well.
I'd really try hard to translate it myself as to not lose any of those traits upon doing it.
If it's a language you don't really know well, you'd have no choice though.
I doubt anyone knows what you wanted to say better than yourself. Even the most skilled translator can miss some fine points you wanted to express. As someone who has seen quite a number of bad translations, I'd never let anyone translate it into a language I know well enough to translate myself. To help, maybe, to edit and give a hand with some subtler points of language, yes, but the whole translation, no.
I'm reading a book right now in English and was surprised to find it in the bookstore translated into Croatian, so I flipped through it and I literally shuddered. It wasn't that it was badly translated, per se, but since it's written in first person, the voice was completely different. It wasn't the same character anymore. I know some things get lost in translation, but this felt like a completely different character was telling the same story. Not to mention that some names were Croationized while most didn't. You just don't do that, you either do it all or none at all.
There are just as much of bad translators out there as there are good ones, it's a lottery which one you would ran into. The ones that have actually lived in a foreign country and are truly fluent in that foreign language are really rare. Translator also needs to have a flair for writing, because it's not all literal translation, sometimes you need to be creative to translate phrases and sentence structures that don't even exist in the other language, and still keep the original meaning in the original voice and style. It's not straightforward. So who better to do it than the original author?
I was instructed by multiple Princeton professors that one's native language is the only acceptable target for a self-produced literary translation. (Of course, not everyone obeys these rules--but even the Nabokovs suffered for it.)
If the "second language" is your native language, I'd say go for it.