Anki (from the Japanese「暗記」, meaning "memorization") is a very versatile open-source SRS (Spaced Repetition System) flashcard program, particularly useful for the study of foreign languages. For those not acquainted with the concept and/or the software, I am sure many good introductory explanations may be found online. I will share here some of my personal decks, made with the intent of acquiring some basic knowledge on the target language, so as to be able to read, or at least get the gist of, mathematical papers written in it.
vokabular.apkg: A 584-card deck made out of the German-English vocabulary at the end of Edmund Landau's 4th edition "Grundlagen der Analysis" (New York: Chelsea Publishing, 1965). This is a classical book recommended for students seeking to learn mathematical German.
As a native speaker of Portuguese, I believe that, for native speakers of Indo-European languages in general, it is technically impossible to acquire the ability of skimming through a mathematical text in Japanese without at least some basic to intermediate knowledge on Japanese language in general. A native English speaker might be able to understand a paper in French with little to no knowledge of French grammar, besides some specific logical words such as "alors" and "soit"; and for a native Spanish or Portuguese speaker, the situation would be even better. Japanese, however, is an entirely different beast. As an example, amongst
one can easily spot the odd one out. Familiarity with the contents of Genki I & II is most likely enough to make the following decks useful:
Heisig 漢字 [xx_10].apkg: A bundle of 11 decks totalling 2042 cards (separated into 10 decks of 200 + 1 deck of 42) consisting of the Kanji listed in James W. Heisig's 4th edition "Remembering the Kanji vol. I" (Tokyo: Japan Publications Trading Co., Ltd., 2001), maintaining the order of the book but excluding pure primitive elements.
en-ja_zagier.apkg: A 471-card deck made out of Don Zagier's "English-Japanese dictionary for mathematical terminology", Japan Intelligencer, Springer-Verlag (1990), pp. 74-77.