NEED FOR REVISIONS
Bible revisions are caused by the need to:
correct previous translation errors
update the language
incorporate new discoveries from scholarship
or a combination of these.

LANGUAGE CHANGE
Languages change and Bible revisions need to happen to keep pace with those changes e.g.
words become obsolete
words change their meaning
words change their grammatical forms
language trends

What might seem an appropriate word at the time of translation may become loaded with an irrelevant meaning at a future time, or may become archaic or even obsolete.

ARCHAIC LANGUAGE
As languages change many words drop out of use or may be replaced by more common words. A word may be considered archaic whilst still used in some contexts. Grammar and inflections may also change. Over time these changes may result in the need for a revision of a previous translation.

The King James Version of 1611 includes many:
obsolete words which are no longer used but are still understandable e.g. winebibber and yokefellow;
obsolete forms of words such as "kine" as the plural for "cow", and
obsolete inflectional endings -eth and -est.

AMBIGUOUS LANGUAGE
As languages change many words may change their meaning, or develop new meanings in new contexts. Sometimes words broaden their meaning and sometimes words narrow their meaning. As such many words which may have been good translations at one point in time may now longer be the best translations and a revision is required.

The King James Version also has many ambiguous English words where the word still is used but the meanings have changed e.g.
translate (Hebrews 11.5) meant to go from one place to another but now means to go from one language to another ,
outlandish (Nehemiah 13.26) meant foreign but now means strange.
These are more of a problem than obsolete or archaic words because people can easily misunderstand what the verses with those words in mean.
ladies walking in the street

LANGUAGE TRENDS
Sometimes the use of languages may change without the words changing themselves e.g. a language may have a trend towards informality.

An example of a language trend in English that has influenced modern translations is that of inclusive language. Where appropriate and retaining the meaning of the original texts, many male-orientated words have been replaced by gender-neutral words e.g. in the King James Version in Matthew 4:19 when Jesus said "I will make you fishers of men", many modern translations such as the CEV and GNB and say "people" instead of "men".

REVISIONS
Examples of modern revisions are the New Revised Standard Version (NRSV) and the English Standard Version (ESV) which are revisions of the Revised Standard Version (RSV) which itself is a revision.