Immersion and Open-mindedness
My first attempt at helping with translation was a simple spelling correction (Russian Mountan to Russian Mountain). I was surprised when someone changed it to "Roller Coaster" when it was obviously the proper name of a particular roller coaster.
I did some searching and found that there's a roller coaster called Montaña Rusa, and I was SURE that the user had just gotten confused, so I changed it back and posted on his wall with an explanation.
He politely explained his perspective and shared some links where others had used the same translation. I still thought he was wrong...until I found out I was wrong.
In one of those strange quirks of language, Russian Mountain isn't Russian Mountain. It's roller coaster.
Here's the reason I found: The oldest roller coasters are believed to have originated from the so-called "Russian Mountains", which were specially constructed hills of ice, located especially around Saint Petersburg. Built in the 15th century, the slides were built to a height of between 70 and 80 feet (24 m), consisted of a 50 degree drop, and were reinforced by wooden supports. "Russian mountains" remains the term for roller coasters in many languages.
It was probably one of the best mistakes I could have made early on to remind me of all the idiomatic history that exists in other languages, and that even when I'm sure I'm right, there's still plenty of room to be wrong.
I find Wikipedia to be useful for idiomatic or idiosyncratic terms like that. Search the source-language Wikipedia for the term, then look on the sidebar for the equivalent article in the target language.
Although in this case you could also just use Wiktionary:
Incidentally, Russians apparently call roller coasters "American mountains". http://ru.wikipedia.org/wiki/%D0%90%D0%BC%D0%B5%D1%80%D0%B8%D0%BA%D0%B0%D0%BD%D1%81%D0%BA%D0%B8%D0%B5_%D0%B3%D0%BE%D1%80%D0%BA%D0%B8