In English, we can say
it's important to translate some words
some words are important to translate.
Why don't we say
some words are important to be translated?
Passive voice is used in certain cases. Overusing and exaggerating is a big mistake. In this case "It's important to translate some words", there's no need to change the sentence to passive, since the sentence is not personal. One chief usage of passive voice is avoiding personal sentences.
For example, when giving driving instructions:
First, you must set your seat to the most comfortable situation.
Then, you must set your rear-view mirror and side mirrors.
Next, your must fasten your belt.
You could paraphrase above like:
First, the seat must be set to the most comfortable situation.
Then, the rear-view mirror and side mirrors must be set.
Next, the seatbelt must be fastened.
This is a formal text, so it is possbile to use passive voice. However, when it comes to scientific texts, using pssive voice against personal sentnces is a prerequisite.
Like mentioned, you should avoid overusing passive sentences unless neccessary.
P.S.: In your example, "it's important to translate some words.", the sentence is already impersonal. Hence, no need to rewite it in passive form.