Learn English – “Shall” and “will” in legal requirements

I don't remember how I learned this, and I can't find a reference just now, but the peculiar custom of redundancy in our legal documents dates back to medieval England. The Norman conquest of 1066 put a French-speaking king and nobility in charge of an English-speaking people. The English courts at the time were extremely sensitive to detail and would throw out a petition for something as minor as a misspelling, so getting every detail right was crucial. Thus, lawyers developed a habit of incorporating English synonyms for key French words (or it might have been the reverse; memory fails me on that detail). This is how we get phrases like null and void and cease and desist. Since American law (except in the state of Louisiana) is based on English common law, the U.S. inherited this custom. Over time, I suspect the legal professional largely forgot exactly why it was building all this redundancy into its documents and "decided" it was as a general matter of belt-and-suspenders caution.

EDIT: I finally found a reference of sorts at Wikipedia:

David Crystal (2004) explains a stylistic influence upon English legal language. During the Medieval period lawyers used a mixture of Latin, French and English. To avoid ambiguity lawyers often offered pairs of words from different languages. Sometimes there was little ambiguity to resolve and the pairs merely gave greater emphasis, becoming a stylistic habit. This is a feature of legal style that continues to the present day. Examples of mixed language doublets are: "breaking and entering" (English/French), "fit and proper" (English/French), "lands and tenements" (English/French), "will and testament" (English/Latin). Examples of English-only doublets are: "let and hindrance", "have and hold."

This is so called "legalese". A dialect used only in contracts, law documents and other court and law related sources. Not only it's valid English, it's written in such a way as to not leave any ambiguities, or room for interpretation, using phrases that don't occur in everyday English, but have specific properties of describing places, moments, locations without leaving room for ambiguity. "Whereas", "Herein" or "thereof" are quite uncommon in normal English, but abundant in legalese.

Think of it more like english-as-computer-language, than english usable for speaking; a trained lawyer can understand it fluently but it's very difficult to read for normal people. Ambiguous wording could be challenged in court — arguments about that can drag into months until the opponent drops the case discouraged by the opposite side taking every entry open for interpretation the opposite way it was intended, so lawyers use so called "boilerplates", document patterns used over and over, that were tested in court as leaving no doubts or ambiguities exploitable by opponents, and just fill in the plaintiff names, dates, objects of the cases, and submit that to the court or file away as legally binding contracts.

Answering:

1. Yes, that's used pretty much everywhere. People who use a different language in their legal documents open themselves to irrelevant, lengthy attacks when using these in court — a tactic to wear off the opponent by dragging the case indefinitely becomes viable.

2. As far as I know, "legalese" evolves much slower than mainstream English, so yes, a very similar language was used 100 years ago. Not only that, lots of words that fell out of use of mainstream English still live through legalese, their contemporary counterparts being more ambiguous, or just through tradition.

3. It's correct, though horrible English. Grammar errors are an invitation for discussion "what the author intended", "what the sentence should mean" and as such, avoided at all cost. Still, the style (e.g. repetition, run-on sentences) is completely disregarded in favor of adherence to the "boilerplate".