If you are applying for a U.S. visa, green card, or other immigration benefit, you will no doubt be asked to submit various documents. For example, you will likely need to prove your identity and nationality using your birth certificate. If you're applying based on marriage to a U.S. citizen or resident, or you have a spouse who will be applying to immigrate along with you, you'll need to supply a marriage certificate, plus death or divorce decrees to prove that any past marriages were legally ended. The list goes on.
However, if the documents you are submitting are in a language other than English, you might need to have them translated. (The exception would be if you are dealing with a U.S consulate that specifically assures you that it accepts documents in the language of that country.)
Failure to submit a translation that is up to the standards of U.S. immigration authorities can result in denial of your application. If a translation is required, here is how to deal with this.
You will need to submit both:
A copy of the original document is needed to demonstrate that it's the real thing. Even if the immigration authorities can't read what it says, they need to see what it looks like, and compare it to internal guidelines regarding what constitutes an acceptable document from your country. (See the Department of State's Country Reciprocity Schedule for a list of what documents it knows to be available and will therefore accept as legal from various countries.)
If, for example, your copy of a document is missing the government stamps that the immigration officials are accustomed to seeing, it might be rejected.
Also, in most situations you'll want to use a "long-form" version of your birth certificate, even if your country also does "short-form" versions. (The key issue is whether the version in question has all the information required to substantiate your claim, such as that you are someone's sibling; in which case a birth certificate that's complete enough to show parents' names will be required.)
A "word-for-word" translation is just what it sounds like: Not a summary, but an exact transcription of every word on the document, even if the words seem irrelevant. You can read more about the U.S. Citizenship and Immigration Services (USCIS) document translation policies within its Policy Manual.
You do not necessarily need to spend money hiring a certified translator. Any trustworthy friend who is fluent in English and the language of the document and is not your close relative is allowed to do the job.
That person will, after typing out the (word-for-word) translated text, want to add the following language at the bottom, and sign it. This includes a promise that the person knows how to translate, and turns the document into what's legally known as a "certified translation."
I certify that I am competent to translate from [fill in the language of the document] to English and that the above [identify the document and to whom it pertains; for example, "Birth Certificate of Maritza Malakoff"] is a complete and accurate translation to the best of my knowledge and belief.
Signed: [translator's full name]
If you prefer, however, you can hire a professional translator to prepare this. That person should also add the same certification at the bottom of the translation.