The Internationale/Performing and respecting copyright
Though The Internationale is often performed and sung to resist repression, it is not automatically in the public domain, so respecting others' copyright is still important.
After Eugène Pottier died in 1887, Gustave Delory, once the Lille mayor in France, once acquired the copyright of his French lyrics dated in 1871 through the songwriter G B Clement having bought it from Pottier's widow. It is in the public domain essentially everywhere in the world.
The first edition of The Internationale with Pierre De Geyter's music showed the composer as his family name (Degeyter) to save his job unsuccessfully. Pierre's brother Adolphe was once considered the "composer" due to false copyright claim. This was disproved in 1922 when the French court accepted Adolphe's 1916 suicide note confessing the fraud as new evidence to award the copyright to Pierre. However, the Soviet Russia already adopted The Internationale as the national anthem in 1917 without knowing the real composer yet. After the Soviet Union discovered the real composer in 1927, Stalin awarded Pierre a Soviet state pension to possibly compensate for his copyright. However, the Soviet Union had no international copyright relations at that time.
After Pierre died in 1932, a film director in France in 2005 was asked to pay 1000 euro for whistling the song for seven seconds. His music of The Internationale is expected to remain copyrighted in France until October 2017. The calculation is based on year 1932 when he died, plus 70 years through year end, plus, for musical works, 6 years and 152 days to compensate for World War I and 8 years and 120 days to compensate for World War II respectively:
1932 Common Era + 70 years until year end + 6 years 152 days + 8 years 120 days ========================= 2016 year end + 272 days ========================= 2017 September 29
Please check your national and regional copyright laws and regulations to see whether the music is in the public domain. If you are in a country or area where the copyright length is limited to an author's lifetime plus up to 80 years, the French copyright length is no longer relevant. However, if you are in France or a country copyrighting for an author's lifetime plus more than 80 years, please be careful before performing The Internationale.
Without affecting the copyright of original works being based on, translated lyrics are derivative works with separate copyrights. Depending on which language version you would like to use, always respect others' copyright. For example, no matter how popular Billy Bragg's modern English version may be, his copyright permission has not released his work into the public domain.
Other legal issues
Besides any copyright considerations, the legality to perform any specific lyrics may vary among countries and areas. In countries and areas respecting freedom of speeches, publicly singing the third French verse (or its translations) to criticize the governments and laws may be okay, but others suppressing freedom of speeches may consider this verse unacceptable or even unlawful. Furthermore, publicly singing the fifth French verse (or its translations), mentioning soldiers going on strike, breaking the ranks, and shooting one's own generals, in any military installations may be unwise or even unlawful as inciting military disorder. After all, before performing The Internationale, please check the legality in your country or area to be sure.