Japanese the language qua language is relatively easy from a language agnostic perspective. Formality levels are tricky, but the phonology is fairly simple (very few "weird" sounds) and the grammar is on the regular side.
The writing system on the other hand... IMO the worst used by any major language in the world. Graft a logographic system (already a bad choice to start) from an isolating language onto a highly synthetic verb system, necessitating a whole extra syllabary. Evolve numerous "readings" of each logogram, depending on etymology and history. Then tack on a 2nd syllabary for abstruse historical reasons.
> If the seemingly arbitrary and unique assignment of pronunciations to common combinations of Kanji frustrates you—[...]—and leave you wondering why anyone would do such a thing, concluding that Japanese has the worst writing system ever, rest assured that they don't have the worst ever. They just have the worst writing system since the Hittites.
Cuneiform signs can be employed in three functions: syllabograms, Akkadograms or Sumerograms. Syllabograms are characters that represent a syllable. Akkadograms and Sumerograms are ideograms originally from the earlier Akkadian or Sumerian orthography respectively, but not intended to be pronounced as in the original language; Sumerograms are mostly ideograms and determiners. ... Thus, the sign GI 𒄀 can be used (and transcribed) in three ways, as the Hittite syllable gi (also ge); in the Akkadian spelling QÈ-RU-UB of the preposition "near" as QÈ, and as the Sumerian ideogram GI for "tube" also in superscript, GI, when used as a determiner.
The writing system on the other hand... IMO the worst used by any major language in the world. Graft a logographic system (already a bad choice to start) from an isolating language onto a highly synthetic verb system, necessitating a whole extra syllabary. Evolve numerous "readings" of each logogram, depending on etymology and history. Then tack on a 2nd syllabary for abstruse historical reasons.