1) The Internet and Public Domain
“You have a blog, it is meant to be shared, it’s in the public domain, so it’s not plagiarism,” - Atty. Hector A. Villacorta, Chief of Staff of Sen. Sotto.
Just because something is on the Internet doesn't mean it's part of the Public Domain. They are actually protected by copyright (and the Philippines is one of the members of the World International Property Organization). Some works on the Internet fall under the Creative Commons, but such works are indicated as such, using the corresponding Creative Commons license, and requires attribution.
Tip: When in doubt, or if there is no indication whether a work falls under Public Domain or the Creative Commons, assume that it is protected by copyright.
Recommended Reading: 10 common misconceptions about the public domain.
Further Reading on the Controversy: Something new to Sottocopy.
2) Translation and Copyright
While there is originality and creativity in the act of translation, it is considered derivative work, and "only the copyright owner can authorize a translation that will be distributed." Considering Sen. Sotto a) claimed that the speech was his, b) offered no attribution, and c) did not have permission from the copyright owner, the speech was in violation of copyright laws—assuming that the speech in question falls under copyright. However, the text falls under Public Domain, so is a valid derivative work. Unfortunately, those coming to Sen. Sotto's defense neglect to mention this (whether his actions were ethical or moral is another matter).
Tip: Short of Fair Use (which in itself is debatable depending on the context) or Public Domain, translations without permission are in violation of copyright.
Recommended Reading: Online Translation - Dealing with Copyright and Plagiarism Issues Part I - Idiot's Guide to Online Copyright Issues.
Further Reading on the Controversy: Sotto apologizes to Kennedy family but denies plagiarizing speeches and “#Sinotto: Copyright over Translations”.
3) Laws and Copying
This is permissible because such laws are usually not protected by copyright (at least that is the case with US Laws). Suffice to say, texts of legal nature are excluded under Philippine Copyright Law.
Tip: If the work falls under the Public Domain, you can use it. Just be aware that works protected by Copyright and those that fall under Public Domain vary from country to country.
Recommended Reading: The Public Domain.
Further Reading on the Controversy: Sotto on apology call: Huh, for what?