As a translator, it is all too easy to let the rules of the source language infiltrate the target language!

This is especially true when translating from German. (German always uses commas to separate relative clauses from the main clause).

The key here is to determine whether the relative clause is defining or non-defining; this will tell you whether or not you need to use a pair of commas to separate it from the main clause.

Defining relative clauses

Defining relative clauses give information which identifies the noun being referred to. They tell you which person or thing is meant.

They come immediately after the nouns they refer to. There is no pause in speech, so no comma is used in writing:
• The boy (whom) I dated when I was at school has now married my best friend.
• The shares (which) he bought when he joined the company are now worthless.

You can tell that these relative clauses define the noun they refer to because if you leave these clauses out, the sentences do not convey much meaning:
• The boy has now married my best friend. (Which boy?)
• The shares are now worthless. (Which shares?)

Non-defining relative clauses

Non-defining relative clauses give information which, although it may be informative, does not identity what is being talked about. They simply add to your knowledge of a person or thing that has already been identified.

Non-defining relative clauses are normally marked by pauses in speech and therefore also by commas in writing:
• Deborah, who was my closest friend in primary school, has now moved to France.
• The third Star Wars film, which has only been in cinemas for a week, has been very popular.

If these non-defining relative clauses are removed, the sentences still make perfect sense and convey the essential information:
• Deborah has moved to France.
• The third Star Wars film has been very popular.

A handy quiz on relative clauses can be found at – http://www.languagelink.ru/e/tefl/miscellaneous.php#2