'internal law' is a correct and usable phrase in written English.
You can use it to refer to laws which are specific to a particular organization or country, as opposed to international law. For example, "The company recently revised its internal law regarding employee conduct."
In dictum in Hudson v. Guestier, 4 Cranch 293, 294, 2 L.Ed. 625, Chief Justice Marshall declared that one nation must recognize the act of the sovereign power of another, so long as it has jurisdiction under international law, even if it is improper according to the internal law of the latter state.
"The police force is largely used for internal law and order, traffic, the drug trade.
Security expenditures for both external defense and internal law and order account for major shares of government expenditures.
The herringbone pattern is geometrically described and the internal law of composition of the periodic cell is defined.
Indeed, he argues that modern capitalism has an internal law of motion that leads, not inexorably but generally, toward less equal outcomes.
He said the country's need for foreign investment, in particular, meant that "we have to improve our internal law and order situation".
The contracting states to the Warsaw convention seek to reduce and eliminate problems of conflict of laws by agreeing to adopt uniform rules in their internal laws governing the international carriage of persons, baggage, or cargo by aircraft.
He also said it meant "the Mexican state will be harmonizing its internal laws with those expected by" international human rights accords.
"The authors may not fully understand that in international law, governments represent the entirety of their respective states, are responsible for the conduct of foreign affairs, are required to fulfill the obligations they undertake with other states and may not invoke their internal laws as justification for a failure to perform their international obligations," Zarif was quoted as saying.
"It is," Lichtenstein reports, still able to use the present tense, "a secret, private, hidden world" with "a strict set of unspoken internal laws".
He created beings and let them develop according to internal laws which He gave every one, so they would develop, so they would reach maturity".
