Notice that I translated the 就 (취) in the final sentence as "that is" (곧), which is one of the meanings of the character. However, Koreans have translated the 就 (취) in this sentence as 나아가다, which means "to go forward" or "to proceed to." That is also a meaning of the character, but it does not really make sense in the sentence here. Here is how Koreans translate the Chinese:
近墨者黑 People (者) near (近) ink sticks (墨) become black (黑). 近朱者赤 People (者) near (近) cinnabar (朱) become red (赤). 居必擇隣 When one takes up residence (居), one must (必) select (擇) neighbors (隣). 就必有德 That is (就), they must (必) have (有) virtue (德).
나아갈 때엔 반드시 덕 있는 사람에게 가라
When you approach, be sure to go to people of virtue.I think my translation of 就 (취) is correct. It fact, 就 seems to be a synonym of the character 卽 (즉), which also means 곧 and 나아가다.
In China, they write "that is" as 就是 (취시) or 卽 (즉), which is more evidence that 就 should be translated as "that is" in the above case.
UPDATE: I now think the original Korean translation was correct since the Chinese philosopher Sunja (荀子 - 순자), which the Chinese pronounce as Xun Zi, said something very similar, as is written in the text "Encouraging Learning" (勸學 - 권학).
The 也 (야) character at the end of the above passage marks the end of the sentence, acting as a kind of period.故君子居必擇鄉，遊必就士所以防邪辟而近中正也.
Therefore (故), when a gentleman (君子) takes up residence (居), he must (必) carefully select (擇) the village (鄉), and when he associates (遊), he must (必) approach (就) educated men (士). In this way (所以), he guards against (防) wickedness (邪) and unfairness (辟) and (而) is nearer to (近) balance (中) and correctness (正).