A written grant by the sovereign or legislative power of a country, by
which a body such as a borough, company, or university is created or
its rights and privileges defined:
1.3 British A policy or law regarded as enabling people to engage more easily in a specified undesirable activity:
In its broadest sense, a charter gives permission to operate under the specified conditions of a higher authority.
The more common British expression is rogue's charter, implying that a law gives permission for rogues to operate freely. The first use available online is a Law Review in 1860:
Well indeed it said that "the case showed how the working classes
might be wronged by these companies!" Yes, here is Limited Liability
in practice. Did we err in calling it The Rougue's Charter?
A more recent use in The Comparative Law Yearbook of International Business:
Such a proposition would indeed establish a new rogue's charter: the
poorer the defendant and the more his wrongful diversion of the
plaintiffs business to himself is injuring the plaintiff, the smaller
would be the prospects of gaining an injunction against him.
Another example with a small morphological shift from Citizens Advice in 2011:
Plans unveiled by Business Secretary Vince Cable today to water down
workplace rights protecting millions of British workers against
exploitation have been branded a ‘rogues’ charter’ by Citizens Advice...
Ministers have said they want to create a level playing field that is
fair to workers and decent employers alike. But tearing up employment
protection will not stop rogue employers gaining an unfair advantage
over law-abiding competitors by exploiting their workforce.
The concern was that new laws would empower rogue employers to exploit the workforce.
Another example of from a 2002 article in The London Evening Standard:
LAWS that give investors protection from unscrupulous companies
floating on the London stock market will vanish under a rogues'
charter proposed by the European Commission.
The article goes on to demonstrate that the existing laws are necessary, but the European Commission is trying to empower unethical players with a new law.
The legal connotations become very clear from its common use. Since crook is an informal expression for a subset of rogue, the expression crook's charter seems clear enough, but one might question the legitimacy of moving the application from laws to the behavior pattern within an industry.
The philosophical obstacle of that shift is probably quite large in a lawyer's mind. The linguistic obstacle in Everyman's mind is much smaller. As individuals and groups, our behavior offers implicit permission for the people around us to behave in a particular manner.
So the sentence under consideration could easily be interpreted:
Non-translators should be aware that the trading conditions for dishonest translation and interpreting companies are optimum, in other
words, the translation business itself gives permission to
An implied definition of crook's charter from that usage in the context of its linguistic origin:
A condition or moral atmosphere that enables undesirable activity.