A rolling stone gathers no moss.English speakers generally interpret this expression positively - staying in one place for too long indicates stagnancy, staleness, and an unwillingness to tackle challenges or new experiences. Hence, a stone in constant motion is a picture of vibrancy and freshness. It denotes someone who is free because he's not tied down.
The Japanese and Koreans have a virtually identical proverb; however, its connotation is largely negative. Being described as a "rolling stone" would indicate that a person lacked maturity and commitment, since he was unable to stay in one place long enough to form roots or build a foundation.
Of course, the differing perceptions of the same proverb illustrate the role culture plays in understanding languages. In addition to linguistic capabilities, translators must possess more than a passing familiarity with the culture(s) of the languages they are dealing with, in order to avoid potential confusion, misunderstandings, and other faux pas.
In English, when we have eaten enough, we announce "I'm full." In Norwegian, however, "Jeg er full" would be the equivalent of saying, "I'm drunk." A better way to phrase it would be, "Jeg er mett" ("I'm satisfied").
English speakers say something like "I'm hot" to indicate that they are feeling the effects of temperature. However, in German, "Ich bin heiss" has sexual connotations. "Es geht mir heiss" (lit., "it goes me hot") is decidedly safer.
Not all phrases are potentially confusing; sometimes, a word picture is employed that is comprehensible even though it is not exactly how English speakers would say it. The Norwegian equivalent of "like two peas in a pod" is "like som to dråper vann" (like two drops of water) - perfectly understandable despite its differences from the English expression. Similarly, English speakers talk about "sleeping like a log/baby," whereas Norwegians and Germans both say "sleeping like a stone."
Needless to say, I think it is interesting to learn different languages and become familiar with the various ways of expressing oneself. Knowing more than one language gives a person a richness that is simply unavailable to monolingual speakers. In closing:
What do you call someone who speaks three languages?
What do you call someone who speaks two languages?
What do you call someone who speaks one language?