I would be interested to know how well do these 'internationals' speak Japanese or any other language other than their native language. I am in no place to laugh at the way somebody swims, as I cannot swim myself.

I am a native English speaker, but fortunate enough to grow up in a household that speaks another language. English is currently the lingua franca, mainly because of the size of the British Empire, and the global influence of USA. However, things could have been different. I am no expert in History, but if Britain lost the battle of Pondicherry to France, then India would have been a French colony and the French would have been the greater influence in India, Sri Lanka and neighbouring countries. If Hitler and his allies won World War 2 would Britain be speaking German today? Who knows? The world is changing, and constantly changes, new powers rise and old powers fall.

Yes, most resources are available in English, both online and offline; and the expansion of the internet has resulted in the importance of English in this globalised society. However, I will never fully understand my Sri Lankan Tamil culture if I didn't learn Tamil. Ancient Tamil literature isn't the same when translated into English (look at the Thirrukural for example). 

Yes English is useful, English is important, but to mock somebody inability to speak English shows lack of understanding. One should look at themselves first. WHen I visited Japan, nobody mocked my basic spoken Japanese, just like how I wouldn't really laugh at a Japanese tourist asking me for directions in their broken English. 

As I said earlier, I can't really laugh at the way somebody swims because I cannot swim myself. Can the person mocking the Japanese person's English speak fluent Japanese themselves?

I am not sure about Japanese, but if it is comparable to Korean, I think I can understand the situation. Here in the Netherlands everybody speaks English. Also older people of say 75 and children of 10 years old. For us it is very easy because our language has some similarities with English, we watch English television, we hear English music. So people tend to think that what is easy for them must be easy for other people as well. And many people in my company complained about the bad English of our Korean colleagues in a joint venture. But when I tried to teach myself Korean I understood how difficult a language from a total different language tree branch can be. I did not ever dared to complain about their bad English which clearly out stands my Korean.

I don't blame Japanese for not speaking English well, but I do blame Japanese teachers for teaching English so poorly. I taught in Japanese public schools for 6 years, three years in high schools and three years in junior high schools. When I taught 1st year junior high students, they learned standard English pronunciation very quickly and easily. However if they were in my class after one or two years of English, they had already learned so many bad habits that it was hard for them to learn to speak English clearly.

The problem, as Patti commented earlier, is with "katakana pronunciation" in English.  Even some of the best teachers I met in Japan tried to "help" students by writing katakana over the English words. In this way, "ball" becomes two syllables, "apple" becomes three syllables, and a sentence such as "I want to learn to speak English" (eight syllables) ends up spoken as 14 (or is it 15?) syllables.

Of course, English IS quite difficult to pronounce clearly without help. Japanese is quite a bit easier. For example, I had an Australian colleague who, although married to a Japanese man, spoke Japanese with the worst pronunciation possible. It was hard to know sometimes if she was even trying to speak Japanese! But then she took a Japanese class, learned hiragana, and in just one week she had completely transformed her Japanese pronunciation. Unfortunately, due to strange English spellings (for example the vowels of book, soon, and flood are all pronounced differently!) Japanese students have a much greater challenge. 

When I left Japan in 1999, things were slowly improving, but there were still many teachers who seemed unwilling to try anything different. I hope things have changed since I left.

I think most people make fun not of your English level, but your pronunciation and accent.

When Japanese start to learn English they often add or remove some sounds, so it's easier for them to say - well, everyone does that. You often translate words to Katakana:
Light becomes Raito
Waiter becomes Ueetaa
Soccer becomes Sakka, etc. 
This sometimes makes words not understandable. And the most important thing in communication is to be understood. 

But, it's not like people make fun of you because you often can't speak properly. Japanese pronunciation of English is just so different from other accents, it makes people smile :)
I also have a strong Slavic accent and people make fun of it sometimes. It's normal. Just let them get used to it and work on your pronunciation.

If someone makes fun of you for speaking a language you are not a native of here is a good response:

"Wow your x language is sooo funny/bad!"

"Well, let's speak in my native language then we won't have that problem anymore."

"But.. but I can't speak your language"

"That's what I thought (sassy face)"

you just put them in their place lol! 

In all honesty, that sort of disrespect is formed in a lack of knowledge. There are plenty of people, especially here in the USA, that have never experienced learning a new language, so their empathy is almost non-existent, unfortunately.