I hear some people say Spanish is hard but that looks tame in comparison to Japanese since first of all Spanish uses the Latin Alphabet with additional letters while Japanese does NOT use that at all (due to them having Kanji, Hiragana & Katakana). The reason why Spanish by some is considered “easy” are the amount of cognates present (i.e. reality > realidad) but the same word in Japanese translates to 現実 which is different, you get the picture.
The sentence structure in Japanese differs from both Spanish & English as it’s SOV while both Spanish & English are SVO that can screw speakers of ES & EN at first as it’s reverse of both languages, so keep in mind. Like this:
The real challenge for native speakers of both Spanish & English is Kanji as it’s logographic and the numerous readings a single character has (take into account of nanori, kunyomi & onyomi) which isn’t the case for an English speaker learning Spanish as the alphabet and writing systems are basically the same. I mean there are elements of Spanish that make it hard to learn (gender cases, subjunctive mood, verb conjugations, etc).
I mean, why do some people consider Spanish hard despite it using the same alphabet? (Although they are NOT part of the same linguistic branch, since English is considered Germanic like Dutch while Spanish is part of the Romance language group like Portuguese). But, in saying that: does that still make Japanese hard or rather simple when you take grammar, writing system, levels of politeness or formal speech into account?
i suspect that spanish has japanese beat in this regard because of its relatively larger geographical dissemination makes formality based grammar rules incompatible with each other -- effectively making all incompatible versions technically correct despite literally contradicting each other.
it's one of the reasons why a majority of non-spanish speakers are taught european spanish rather than any of the SIGNIFICANTLY larger versions of spanish that exist.