• I'm less close to fluent in Parisian French than I was a few years ago but it is still my most thoroughly studied language, studied for six years. For a rough approximation of my ability level, let's say I can hold a fair amount of conversations beyond that of a tourist, and I can read Victor Hugo untranslated and get the gist of most sentences... though not too many. Have some familiarity with Québecois, partially owing to my own ancestry.
• I've studied Russian for two years and spent a month in St. Petersburg in a total immersion environment. Consequently I am not anywhere close to fluent but I guess if you threw me back in an immersion setting I'd catch on fast.
• I've studied Mandarin for one year and know about 500 characters, give or take. This is what I've formally studied the most recently so I'm the least rusty.
• I did an intensive study of ancient Greek many years ago but mostly just retain knowledge of alphabet, phonology, and rudimentary grammar. Do not ask me for any help here because I'll probably just flail and make something up.
• I am not remotely fluent in but could probably tell you at least one interesting thing about the following languages: Basque, Cantonese, Esperanto, Finnish, German, Georgian, Guugu Yimidhirr, Hungarian, Icelandic, Inuktitut, Irish-Gaelic, Italian, Japanese, Klingon, Korean, Lakota, Modern Standard Arabic, Old English, Pirahã, Quenya, Sindarin, Spanish, Swahili, Ukrainian, Welsh, Zulu (yes regarding the constructed languages there I am a Tolkien nut but no I would not style myself a philologist as he did and also no I am not remotely a Trekkie)
I leave that for your perusal just as a record of why for example you should not ask me about Mongolian, as that is something I do not list as knowing. Anyway, given my major, my undergraduate thesis has a lot to do with linguistics, philosophy of language, cognitive science, psycholinguistics, all those fancy dandy terms. I'm about to start writing it very soon and it's going to very heavily concern Finnish, Swedish, German, and Russian, as well as touch upon some Balto-Finnic relatives like Saami, Karelian, and Estonian. If anyone could provide me with some ideas about good language-learning sources for the first four (or for the latter three, but it's not as important), that would be great. I'd prefer sources that address things from a linguist's perspective, not necessarily a conversational learning guide, though for just the Finnish that would be good too. The linguist's perspective is especially important for Russian because I'm already acquainted with it.
Thanks for whatever help you can provide! And I look forward to helping other people out if they need it. I love teaching.