Not sure how it compares to mandarin, but simple pronunciation in Japanese leads to the problem that with only 5 vowel sounds, tons of words just sound really similar. It can also be difficult to tell where an unfamiliar word ends and the phrases around it begin. And then if you miss a word at the start of a topic it often won't even be referred to with a pronoun to give you a clue, it just gets dropped entirely.

Several people have mentioned the difficulty of Japanese grammar, and I want to expand on that a little. If you have already learned a second language that's significantly different from your first language, then you probably won't find Japanese grammar to be too confusing. It turns out that there aren't that many different ways for most world languages to organize themselves, so what we often see is that people learning their third or fourth language don't actually find the grammar to be too difficult.

If you want to learn the language efficiently, you need large amounts of input and output, because you have to memorize so many words and patterns and example sentences. And then from time to time you study some grammar to make sure that you know why those example sentences mean what they mean.

For example, other commenters have mentioned that the order of the parts of speech in the sentences for Japanese is quite different from English. That's true. But actually that's not a stumbling block, because you should often be forming sentences by creating variations on sentences that you've already memorized. And if you're doing that, it doesn't take very long to get used to the switched order.

Some new language learners intuitively decide that they should try to formulate the perfect sentence in English first, and then ponder how to translate that to Japanese, in which case they feel like the switched order is problematic... Here, the real problem is their intuition. If they can learn to stop doing that, they will find it much easier to proceed in their studies. But sometimes that's easier said than done.

Japanese pronunciation is quite simple. A word is one or more syllables and a syllable is one of the things represented by hiragana. Learn that, you've got most of the sounds. The exceptions are devoicing of 'i' and 'u' in some contexts, and standalone 'n' changing to 'm' in some cases (pronounced shimbun rather than shinbun as it is spelled). That's about it for that part.

Then, there's pitch accent. You can get this wrong and it almost never matters (yay, context!), but you will sound foreign/weird. Then again, pitch accent is not the same in all dialects so there's that as well.

Japanese sentence order is SOV (I school go) instead of English (SVO). I assume you're talking about being easy to learn as an English speaker since you wrote this post in English.

If we go further down the rabbithole, there are different registers that use different honorifics, verbs, conjugations, and such. It's annoying (personal opinion), but you just need to remember 'say x instead of y in this context'.

Mandarin has more possible syllables and sounds and also has tones. I imagine messing up the tone is also saved by context usually, but it seems more severe than pitch accent mistakes. It seems grammatically more similar to English from what I can tell and lacks verb conjugation. I've only taken one or two lessons, so that's about all I can say.

Chinese native speaker, pretty good at Japanese (passed N1 many years ago). I actually think spoken Mandarin Chinese is a lot easier to learn for most situations except for a complete beginner:

• For a complete beginner, Japanese has one of the (if not the) fewest possible valid pronunciation among all languages. There are literally only ~50 "alphabets" (officially only 48, there are a few weirder non-official ones), all of which are easily pronounceable. Mandarin Chinese also has a pretty restrictive pronunciation set, it's simply that the tones (especially the 3rd) tend to trip ppl up
• Past the complete beginner stage and Japanese becomes noticeably more difficult than Chinese. Japanese grammar is an absolute nightmare, and you do have to know most of the grammar rules; not to mention you can have multiple different ways to pronounce the same word... Whereas Chinese has almost no grammar and overwhelmingly relies on memorizing vocabs, which someone who only wants to speak doesn't even need to worry about how to write them (which is most of what makes it difficult)
• Just to clarify, both Chinese and Japanese are high-context languages (to compensate for way too many words sounding exactly the same), so the fact that a local might not understand you often has less to do with shitty pronunciation, and more to do with that the entire sentence makes no sense. A lot of Chinese ppl understand regional dialects (which are pronounced very differently) just fine

The Chinese dubbed anime thing is for Chinese ppl too. JP has a very robust seiryu (voice actors) industry, and a lot of CN/KR dubs just simply can't catch up with the voice-over quality... A good example, think Genshin Impact: it's a Chinese game but the default VA is JP (edit: to correct myself, it's the de facto VA most ppl use; a lot of Chinese ppl happily switch to JP VA whenever they can). I highly doubt this has anything to do with the language themselves. The language themselves... I've heard some ppl say that spoken Chinese sounds "angry", might have something to do with the tones. Not sure about Japanese...

I grew up with a Mandarin household and only learned Japanese later. I would tend to agree than Mandarin is easier but there are nuances.

Japanese is way easier. Mandarin is tonal and if you don't have an ear for it, it is maddening to talk to natives and they can't even guess what you're trying to say because you can't tell that you're using the rising time instead of the flat high tone.

Personally, I also find the tone restrictive since atonal languages can use musicality in speech as another dimension in emphasis while that would muddy meaning in tonal languages.

That said, Japanese is hard in other ways, but those hurdles are when you get closer to fluency

As someone who has been learning Japanese for a very long time, I can tell confirm that Japanese grammar is quite complicated, as others have said. One example could be that adjective clauses go before the noun, instead of after the noun, which could be hard to wrap one's head around it.

The other issue is that the sentence structure is different from other languages. Japanese language uses Subject-Object-Verb structure instead of Subject-Verb-Object - to put it simply, sentences end with a verb. It could be a problem for a beginner, or even when you get to the intermediate level, where you could start hearing 3 complete sentences before getting to the first verb.

And another potential issue is that there are multiple levels of politeness. Each level changes how you say verbs and some other words. The highest levels even change some verbs to different verbs with the same meaning. But this is mainly issue only when you are planning to live there or work in Japanese company.

I don't know much about Mandarin Chinese other than that it uses different tones to pronounce words. And if you are like me, who doesn't hear those tones, it could be impossible to learn.

I believe learning Japanese pronounciation is going to be easier for some people, but it really depends where you come from. I never had to learn Japanese pronounciation because it is almost identical to my own (slavic) language.

Japanese has fewer sounds, and as an Indian I can already make most of them. On the other hand, the grammar is very subtle and tricky.

As for how they sound, I would say that Japanese sounds warm and energetic, while Mandarin sounds soft and polite.

In addition to being more familiar due to anime, I find Japanese easier to listen to (although I don't understand much) because when transliterated into English it's quite easy to pronounce the words once you get the hang of it. Not even considering the tones, I think there are just fewer sounds in general and they're all easy to learn. It's not hard for an English speaker to understand what words are being spoken even if you don't know what most of them mean.

It depends on what you already know, if you don't know any tonal language already then learning your first tonal language will obviously be an additional hurdle.

That said, Chinese is considerably easier to learn than Japanese in many other ways, such as the basic grammar being remarkably straightforward.

Having learned a lot of Japanese and a little bit of Mandarin, I'd say that Mandarin is easier overall. Pronunciation might be simpler in Japanese, but the grammar is much more complex.

I've never learned Japanese, but I found Mandarin tones very easy to learn. You learn how to say the word one way, one time. Whereas with Japanese, the way you say things changes based on context, and it's going to be hard for a foreigner to learn that. Either way, you're not going to sound natural as a speaker if you start after childhood.