Hello and sorry to take so long answering your question, I hope this post can help with some of what you’re wondering.

You are correct in saying that Meiji Japan used for the basis of their new legal system French and especially German law. This was not only a decision by the new nation’s leaders to emulate a political system they saw as beneficial to their historical moment but also to legitimize themselves in the eyes of observing Western powers. Your question asks about if Japan exported this system to its colonies and I think it’s important here to identify what this system was and what it would be replacing in Japan’s new territories.

Western law is (I will be speaking in broad terms here and encourage anyone more familiar with this to add on to or correct me) primarily identified as the systems of “civil” and “common” law. Civil law traces its history back to Justinian’s Legal Code of the 5th century which provided a codified system to which judges could refer while settling disputes. Common law generally refers to the system that formed over centuries in Medieval England and centers much more around legal precedent formed from local customs that were eventually codified as the law of the land (or region as it were).

The small details aside, what was shared by these Western systems of law were a sense of guaranteed freedoms, privileges, and rights that were based on established law and to which judges were bound to follow. This contrasts with the Sino-Confucian system (again, broad strokes) that was most prominent in territories like Taiwan and Korea. In East Asia, which saw political centralization take place much earlier than in the West, the state’s primary function was the administration of the state, not settling private disputes. When private disputes did arise, they were not settled through claims to rights written out in the law but were rather brought before a judge as a claim that one party had failed to act morally per Confucian texts. In this scenario, although the judge had some regulations to refer to, judges primarily used their own sense of morality honed through familiarity with the classic texts to settle disputes. The judge here was not meting out the law but correcting public morals. Resolutions were not of a legal but a persuasive nature.

The role of local practice in this system must also be acknowledged, but the key difference between the Sino-spheric and Western European traditions is that in East Asia is that these practices were never collected and codified into a legal tool that would decide future conflicts. That is to say, “common law” as was known in the West did not exist in East Asia. This context is important to bear in mind when discussing how these European legal concepts were transmitted via Japan to its colonies.

Taiwan (I am choosing to overlook Hokkaido and the Ryukyu Islands to stay more on topic with OP’s questions), acquired from Qing China in 1895 after the First Sino-Japanese War was placed under the jurisdiction of the Governor-General of Taiwan 台湾総督府(GGT). The GGT was responsible for the administration, legislation, adjudication, and policing of the colony and was given the right to make laws via proclamation. Japanese jurists recognized the difference in manners and customs in Taiwan as reasons that the legal systems between the metropole and colony had to differ. While this was used as a pretense to not apply the Japanese Constitution to Taiwan (indeed, all the colonies, including Hokkaido were classified as gaichi 外地, outside land, and the Constitution did not apply there), it also became a guiding principle for the GGT in legislating as it was recognized that exporting a foreign legal system wholesale over a populace would not be conducive to maintaining social order there. This line of thinking is reflected in the application of Japanese law over Taiwan where it concerned establishing administrative bodies and the criminal code, but preserving local practices in dealing with civil disputes, especially as concerns commercial or family law.