Yes, they really called it that.
Imperialism and racial fears and sex and commerce and legalism mix badly, it turns out.
International Convention for the Suppression of the White Slave Traffic (4 May 1910)
Whoever, in order to gratify the passions of another person, has procured, enticed, or led away, even with her consent, a woman or girl under age, for immoral purposes, shall be punished, notwithstanding that the various acts constituting the offence may have been committed in different countries.
Whoever, in order to gratify the passions of another person, has, by fraud, or by means of violence, threats, abuse of authority, or any other method of compulsion, procured, enticed, or led away a woman or girl over age, for immoral purposes, shall also be punished, notwithstanding that the various acts constituting the offence may have been committed in different countries.
International Convention for the Suppression of the Trafficking of Women and Children (30 September 1921)
The High Contracting Parties agree that, in the event of their not being already Parties to the Agreement of May 18, 1904, and the Convention of May 4, 1910, mentioned above, they will transmit, with the least possible delay, their ratifications of, or adhesions to, those instruments in the manner laid down therein.
The High Contracting Parties agree to take all measures to discover and prosecute persons who are engaged in the traffic in children of both sexes and who commit offences within the meaning of Article i of the Convention of May 4, 1910.
The High Contracting Parties agree to take the necessary steps to secure the punishment of attempts to commit, and, within legal limits, of acts preparatory to the commission of, the offences specified in Articles 1 and 2 of the Convention of May 4, 1910.
Any Member or State signing the present Convention may declare that the signature does not include any or all of its colonies, overseas possessions, protectorates or territories under its sovereignty or authority, and may subsequently adhere separately on behalf of any such colony, overseas possession, protectorate or territory so excluded in its declaration.
Japan: The undersigned delegate of Japan ... declares that his signature does not include Chosen, Taiwan and the leased territory of Kwantung.
The government of Japan eventually acceded to the 1921 Convention in 1925. It expanded the original list of exempt territories to include Japan's South Pacific trust territories and the Japanese half of Sakhalin Island. (Link)
So, according to treaty, someone tricking a Japanese woman or woman residing in Japan into transport abroad to serve as a prostitute, or using force to do same, was illegal.
Tricking a Taiwanese or Korean woman or child, or even having a Taiwanese or Korean child go voluntarily, was not illegal.
If you were in the procurement business, let us say for a large institutional client who also was in charge of regulating said business, where and how would go about your business?
The comfort women system was not sui generis, a product of diseased national mindset. It was in many ways an unintended consequence of international conventions put forth by Europeans attempting to prevent women of European extraction ending up in the brothels of brown-skinned peoples -- and Europeans not being confident they had the resources or legal precedent to extend the writ of those conventions to the many peoples and cultures residing in their colonies. Europeans, because they were racists, unthinkingly opened a huge hole in the first international trafficking agreements -- which Japanese and the Japanese military, because they were not racists, proceeded to exploit.
Imperialism and colonialism were the roots of the problem though. It was these fundamental insults to human dignity and human life that made the best intentions and noble sentiments go wildly astray.