According to the U.S. Copyright Office, "there is no such thing as an 'international copyright' that will automatically protect an author’s writings throughout the world. Protection against unauthorized use in a particular country depends on the national laws of that country. However, most countries offer protection to foreign works under certain conditions that have been greatly simplified by international copyright treaties and conventions. There are two principal international copyright conventions, the Berne Convention for the Protection of Literary and Artistic Works (Berne Convention) and the Universal Copyright Convention (UCC)."
The Berne Convention was first adopted in 1886 to honor the rights of authors who are citizens of countries that have joined the convention. For a summary of rights provided by the Berne Convention, see the UK Copyright Service Fact Sheet.
Copyright questions that pertain to works created in other countries are notoriously difficult to research. This is largely due to the fact that each country has different laws relevant to copyright, and in many cases, different languages.
If you wish to reproduce a significant portion of an author's work, the first step is to identify the copyright holder and request permissions for the use. There is good information on this process from Columbia University Libraries/Information Services Copyright Advisory Office.
Before embarking on an international copyright permissions project, you may want to consider the following alternatives:
You may be able to use a portion of the work in question by claiming fair use. However, be aware that each country's definition of what constitutes fair use may differ from U.S. law.
Can you locate a similar U.S. source with an identifiable copyright holder? If so, contact that rights holder and seek out the appropriate permissions. Or, you might also be able to locate an equivalent source that is in the public domain.
Rethink Your Intended Use
Rather than use the entire work, can you cite a small portion of it, or even paraphrase relevant points? Relying on quotations, paraphrasing, and proper citation methods can often help you avoid the copyright permissions process altogether.