The Interpretation Act 1978 (originally 1889) defines various terms for most Acts in force in England and Wales, and to some extent Northern Ireland and Scotland too. I’ve put a copy (accuracy not guaranteed) online – it should be useful to legal translators both into and out of English with regard to Britain.
6. In any Act, unless the contrary intention appears,
a) words importing the masculine gender include the feminine;
b) words importing the feminine gender include the masculine;
c) words in the singular include the plural and words in the plural include the singular.
Schedule 1 contains a list of words and phrases.
Oath and affidavit include affirmation and declaration, and swear includes affirm and declare.
I understand that affirm (swearing without a Bible or other religious book) is the equivalent of swearing. But what about declare? That refers, apparently, to a statutory declaration in lieu of an oath and other kinds of formal declarations required by some statutes. Some are required to be made before a particular person, for example a magistrate, and the person has to satisfy himself that the person before him is the declarant named in the declaration.
Person includes a body of persons corporate or unincorporate. 
I learnt recently that Person in the German Civil Code also includes not only natural and legal persons, but also associations of individuals that are not legal persons. I don’t know where that is defined in German, though, and I don’t know whether this means it is always safe to translate Person as person.
Writing includes typing, printing, lithography, photography and other modes of representing or reproducing words in a visible form, and expressions referring to writing are construed accordingly.