It can be anything, including places, names, and things.

For me,

Croatian:

tvrda = hard (e.g. hard surface)
Zagreb = Capital of Croatia

Serbian:

Prokuplje = Serbian city (pronounced pro-ku-plieh)
Džigerica = A Serbian dish made with liver (pronounced Jiggerizza)
Zdravo = Serbian greeting, not sure if also used as a goodbye

Spanish:

Tonto = idiot

Romanian:

bună dimineaţa = good morning

Brazilian Portuguese:

Pão = bread (pronounced like "pow" but nasalized.)

European Portuguese:

Espreita = to ambush or to peek (pronounced esh-prai-ta)
Cidade = City (pronounced See-da-de)

Czech:

Vlk = wolf (pronounced like vulk but the U is pronounced like the u in careful)
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There's a ton of others that I currently haven't learned the meaning of yet.

But what are your favorites?

Haha, what a cool thread idea!

I really like the word Metchka in Croatian, meaning cat (I think).

And ya can't really beat the classic omelette au fromage from Dexter's Lab.

The rest is just a bunch of Japanese words I learned in High school.

Baka: fool
Tonndemonai: "No way!"
Shimatta/Kuso:"Darn it/Crap!"

English:
"Ambiguous" (not clear in meaning): added bonus that nobody I know knows what this one means.

Italian:
"Dimenticare" (to forget): it's been so long since I sat in an Italian class that I've forgotten what I liked about that word, but apparently whatever it was good enough to be one of my alternate usernames in several web sites.

Japanese
Renkinjutsushi (Alchemist <3333). Pretty much the only long Japanese word I know by heart.

Italian
Vecchio (Old)
Pomodoro (Tomato, my favorite thing)
Sognare (To dream)
Ciao (Hello, Goodbye)
Attaccato (Attached)

English
Superfluous (more than necessary)
Ingenuity (cleverness)
Discombobulated (Confused)
Fluffernutter (PB&M)

Atatakakunakatta (Japanese, 暖かくなかった or あたたかくなかった), "wasn't warm"

La araña anaranjada (Spanish), "orange spider"

Shenanigans

English

Anarchy (extreme disorder/without government)
Melancholy (deep sadness)
Ludonarrative Dissonence (the disconnect between the player and the character)
Kerfuffle (fight or disturbance)
Applejack(s) (the cereal or pony)

Spanish

Quince (15)
tararear (to la-la-la; to sing to oneself)

Words are fun sometimes. I like this thread.

English:
-DEFICIT (Lack of something)
-DEMONSTRABLE (something you can demonstrate)
-ABSTENTIOUS (not indulging in excess)

Old Norse
Fenrisulfr: meaning Fenris Wolf, the beast destined to devour Odin. It also sounds like sulfur when you slur the syllables.
Gjöll: meaning scream.
Dovahzul
Sovngarde: Skyrim's equivalent of Valhalla, where slain warriors go after death to feast and spar for eternity. Although it isn't clear whether this word is actually in Dovahzul or not, it is definitely fun to say, especially quickly. S'vingaard!
Kruziik: meaning ancient, make sure to roll the r and the z can be pronounced as if German, so more like a ts sound.
German
Feuer: meaning fire.

English:
- ANTIDISESTABLISHMENTARIANISM (Political position that originated in 19th-century Britain, opposes proposals for the disestablishment of the Church of England)

I just love this word. Look at it, just LOOK at it!

English
-Conundrum:
1. a riddle, the answer to which involves a pun or play on words, as What is black and white and read all over? A newspaper.
2. anything that puzzles.

German
Schmetterling
-A butterfly

Du Haust in German word for English means You have or you hate I think

Lyublyu. It's so cute to say. It means love in Russian, I think.