A proper dictionary is helpful for study a language. Many dictionaries are monolingual or bilingual but some dictionaries contain three or more languages. I have seen a cool Japanese-Chinese-English dictionary.
I think a dictionary that contain more than three languages is more suitable for study languages if a learner really wants to study those languages. It also means I think the dictionary isn't useful if a learner doesn't seriously want to study those languages.
Because I study Chinese, Spanish and English, I want a Chinese-Spanish-English dictionary. Although I searched for it in the Internet, only I found "Spanish-English-Chinese Dictionary Of Petroleum". It seems a very useful dictionary... when I build my oil empire.
(Do you want to build your oil empire and lead the world to open the Last World War? Oiligarchy is a cynical game.)
I can't find a three languages dictionary, thus I must buy some bilingual dictionaries. But which pairs of languages are better? Japanese-Chinese(or Spanish), English-Chinese or Spanish-Chinese? I don't know... But bilingual dictionaries without Japanese are quite hard to find in Japan. Of course, I can order it on the Internet, whether I accept shipping cost that can be higher than its price...
This problem is not only the dictionaries, foreign language books except English also aren't easy to find in Japanese bookstores. I looked for "The Art of War" or other useful Chinese/Spanish books in some large bookstores where I bought Oxford Bookworms/Dominoes series and English novels, although I only found very few and less attractive books.
In addition, I have an interest in German language because I like to sing "Panzerlied" and "Auferstanden aus Ruinen". Now I have to spend much effort to study English, Chinese and Spanish, but I wish to study German someday. However German is less popular language than Chinese or Spanish, It means it is more difficult to look for good German books.
If I can't get good foreign language books, I have to study languages in the Internet. Fortunately, after I start to watch "Xiong chumo" animation, my Chinese vocabulary has significantly improved. But I still not meet a good Spanish content. I think I should see more Spanish contents.