By "legal language" I assume that you mean the typical written language found in licenses and similar law-related papers. By "plain" I assume that you mean ordinary spoken language.
Legal language has a purpose of specifying very precisely some terms or rules that people are to follow. Plain language simply cannot give the same amount of precision without using much more time on the specification of the issue.
A typical example in legal language is to introduce entities:
"In the following X refers to yada yada yada yada yada [long text describing the entity X goes here"
Then later in the legal text it is possible to use X instead of the long introduction.
Michele M. Asprey has written: 'Plain language for lawyers' -- subject(s): Legal composition, Usage, Law, Language, English language 'Plain language for lawyers' -- subject(s): Legal composition, Usage, Law, Language, English language
Robert C. Dick has written: 'Legal drafting in plain language' -- subject(s): Legal composition, Law, Language 'Legal drafting' -- subject(s): Legal composition
Language Made Plain was created in 1964.
Language Made Plain has 196 pages.
The ISBN of Language Made Plain is 0-34004-770-4.
The word plain in Portuguese is: "planicie."
A plain everyday language with no pattern would be random and disjointed, lacking any structure or coherence.
Bryan A. Garner has written: 'Black's Law Dictionary (Pocket)' 'Garner on language and writing' -- subject(s): Law, Legal composition, Terminology, Language, Style, Citation of legal authorities, English language 'Black's Law Dictionary' 'Black's Law Dictionary Digital' 'Securities disclosure in plain English' -- subject(s): Language, Securities, Law and legislation, Disclosure of information 'The Winning Brief' -- subject(s): Legal composition, Briefs, Legal briefs 'Black's Law Dictionary, Deluxe Edition in Slipcase'
Prose.
legal
Legal language refers to the language of law and law documents and the words unique to this area of speaking and writing (contracts, legislation, etc).
Rupert Haigh has written: 'Legal English' -- subject(s): Legal composition, Business English, Terminology, Language, Usage, Law, English language 'Legal English' -- subject(s): Business English, English language, Language, Law, Legal composition, Terminology, Usage