Japanese is too big of a language to NOT learn full time. Russian is much simpler in that respect. Because of Japanese's 3 writing systems, I am hight impressed with a Westerner who learns enough Japanese to read and write it! (
Not just katakana). Japanses is rather easy grammar wise, but the writing system is too complicated to make it a
part-time language. Once you learn Cyrillic (which you can learn in a day), you can read ANY Russian word, and can pretty much write any Russian word too. But with Japanese have three writing systems and Kanji having
multiple pronunciations, it's more like a secret code than a national language. I've met quite a few westernersw ho can speak Japanese, but I ave NEVER met a Westerner who can read a Japanese newspaper. You should learn Japanese if you don't mind beng illiterate.