English is the universal language, so it's a global 2nd language.
The problem in Thailand is the Farangs not knowing enough English themselves, as for many here it's also their 2nd language, and they don't bother to learn the proper colloquial Thai language. In addition some Farangs up north that do try to learn, mix the the Issan dialect with the traditional Thai, and that is just one dialect, and painful to listen to a Farang screwing up the language. It's equally painful to listen to a Farang speaking in broken English to a Thai. It does no favors.
A lot of Thais do know English, as well as many other languages. I am Thai, and can speak Japanese, Chinese, English, Spanish and German. How many Farangs can speak my language, with full comprehension? Very few.