I am at a bottleneck or crossroads in my language learning. First of all, I am not a language-learner per se. I pursued Spanish, French, Old Norse (briefly), Latin and Ancient Greek because I love and want to read their literatures. Knowing the language is especially valuable for the best poetry. As for prose, well, I'll leave it at that. I debated between Mandarin and Japanese. Japanese won out because tones shied me off of Mandarin, and, far, far more important, Japanese literature seems to offer more to my taste than Chinese literature (though I confess to a lot of ignorance about both). Haiku alone, coupled with other Japanese poetry, attracts me more to Japanese.
if language focus would be japanese for poetry and literature, perhaps it would help to focus on a specific genre or era with multiple authors in that range? that way you get synergy from the different perspectives.
for example, dōgen zenji was a japanese priest who founded the sōtō school of zen buddhism in the 1200s. he was a prolific writer including poetry. then you could read comments about his work (positive or negative) from others. several students wrote about dōgen's teachings after his death. seen from different perspectives the language study might be more intriguing.