I don't speak another language, but I'm self teaching myself Russian right now... it's a lot easier to write for me (with google translate, unfortunatly... -__-) than pronounce, but I guess it depends on how easily you can pick up a language. Some people can go really easily with it, and some people
could pick it up really easily, but are too lazy too. (aka me) And then there are those who just have flat out trouble learning another language.
For Japanese, I hear that the Kanji is pretty tough... and Chinese you have to worry about all the characters AND the pinyins....um....well you probably won't do Russian, soo.....haha. And you don't want to learn Spanish (I second your opinion)...maybe French or German, like the people before me have said....
Another thing you should look at when picking a languge, is to know someone you can talk to. Like I know people online and in real life who I could speak Russian to, so it would make more sense than Chinese, for me. If you have a friend or someone you know who speaks Swedish, I would say go for it!
But I personally think it would be really cool to do a minor language like Estonian or something... ^^;
You also might want to consider how useful the language will be to you. Spanish would be very useful, but like I said, I second your opinion...
Chinese or Japanese or German would probably be useful to know as well, especially Chinese and Japanese...
I don't know how you will be learning your language(self teach, tutor, friend), but if you do self teach, or even any other kind, I really suggest watching something (a movie, a show, a song, ect.) that you really love and know fairly well in the language.....like sometimes I'll watch Russian Spongebob since I know the words to almost all the episodes and I can see how it would be spoken and the such....just as a helper!
Good look Wolfie! ^ ^