The best free online source, this site primarily covers law reports and law periodicals in English, but major foreign language law publications are also included.
The Bluebook: A Uniform System of Citation, 21st ed. (2020).
The rules provide citation suggestions for foreign and international materials, with specific examples found in the Tables:
Bluebook T2 Foreign Jurisdictions
Beginning with the 21st Edition of The Bluebook, T2 is available free to the general public on this website. Individual country entries are updated on an ongoing basis.