What is the ruling on wearing the Japanese garment called the "yukata," knowing that it is modest and not intended for imitation?

It is not permissible to wear the special clothing of the Japanese or other disbelievers, due to the prohibition of imitating them in what is specific to them. Blameworthy imitation is realized by doing what is specific to disbelievers in terms of customs, with knowledge of that, even if the doer did not intend to imitate them.