The subject 'English' should really be called language. If you were in Japan and you were doing the exact same subject it wouldn't be called 'Japanese', amirite?

In Japan, the "exact same subject" would be English, technically speaking. The Japanese equivalent would be Japanese, but it obviously wouldn't be exactly the same. Also, they call it English because it is and analysis of the English language. If they just called it Language, you coyld be analyzing Russian for all they care.

But then "Language" class could be any language. In Spain they call their "Language" class Spanish.

In Japan they call it 国語 (it might show a massive cluster fuck of text if your computer doesnthave foreign language settings), and it means "Language Arts".

It can work in the US too.

Every language class teaches the same thing regardless. Any language class will give you basic knowledge of grammar, formatting, spelling, rhetoric skills, and reading skills.

In South Africa it's totally different.
Seeing as we have 11 official
languages and others offered at
school additionally to those, we have
a system based on your Home
Language (though some schools offer more than one in Home
Language level), First Additional
Language and Second Additional
Language. I don't know the limit.
I have Afrikaans Huistaal (Home Language) and English FAL (First Additional Language).

I usually hear it referred to as ELA or language arts, not English.

That's silly. When you learn about the English language, it should be called English. What about places where you learn more than one language at school? In primary school, we learnt three.

No, but if you were in Belgium and you were doing the exact same subject it would be called 'Dutch'. Just saying.

Yes they do. In most countries the class of the national language is just "(National language)". In South America la Clase de Español, in Russia Русский Язык and so on.

Where I am we call it english language arts, ELA for short