This only works for tables of contents created with this feature in Word.

Do not translate the Word table of contents (TOC) at the beginning of the document. First translate the document containing all the chapter headings and sub headings. These will have been given a specific style (Heading1, Heading2, etc), which it is important to keep. When you have finished your document, return to the table of contents. Right click on it. It should then turn grey. In the drop down menu, click on Update field.

It works like magic. Suddenly you've got a translated table of contents.