Esperanto
(en letra mayúscula)

I did see the name capitalized in Spanish as well.
Is it a mistake to capitalize the language name in Spanish?

the names of the languages are not capitalized in Spanish, so wherever you saw it, it was wrong...

Thanks. Well, actually, this is not a simple name of a language, but the name of Zamenhof himself (he called himself "Doktoro Esperanto", and it later became the name of the language). This is why the name Esperanto is usually capitalized, I believe (in addition to the fact that it's a language name). But if you think it should be lowercase in Spanish, then so be it.

@Eldad: If one was referring to Esperanto in that sense, then it might make sense to capitalize it. But if referring to the language, then it wouldn't be capitalized in Spanish.

I'ts like how "god" may or may not be capitalized in English, depending on the context.

@Zifre, the thing is Esperanto is the only language name which is also a name per se, not just like any other regular word in a language (as English, French, German etc. are). This is usually why it is treated as any personal name (which is naturally capitalized).

Of course, if one doesn't know it's a personal name, then it will be treated just like any other language name, i.e. capitalized or not, as the custom is in the language in question.

@Eldad: I think in Spanish it should be capitalized when referring to the person, and not capitalized when referring to the language.

Yes, I agree with you (I re-thought the issue after our short conversation, you, Zifre and myself).

BTW, it practically doesn't refer to Zamenhof anymore, only to the language itself. So it is hardly used as a name, only as a language name (and as Spanish doesn't capitalize language names, it will not capitalize it either).