Each of us constructs our own unique version of the world in our minds, but we don’t necessarily notice everything, at least consciously. The things we see, hear, touch, taste, or smell evoke memories, associations and various trains of thought.
When you learn a foreign language, you are effectively creating a new version of the world in your mind. Everything will have a different name, though it takes a long time to learn all those names and there are likely to be gaps in your vocabulary. One way to overcome this problem is to learn how to describe the things for which you don’t know the words. Another way is to focus on particular subjects and to learn as many of the relevant words as you can. To test your new vocabulary, you could try explaining the subject to someone else and/or writing about it.
Non-english vocab has always been somewhat of a problem for me, until I learned Esperanto. Eo (Esperanto) uses a lot of common roots. From there I am able to jump to thers, likes stepping stones in a pond. Also I try and find the most interesting (possible?) links between words. My friend Jordan, who created Neith, came across the fact that a Manger (where animals eat) sounds a lot like the Eo word Manĝi (to eat). Things like this help me to remember words. I also use a method that I believe Simon has mentioned, imagining the German vocab sitting in Germany (in my imaginary map) and the Latin ones sitting in the Colliseum. (The Italian ones are in Italy) and the Eo ones are in… (As we would say) Volapukejo (because it doesn’t exist, and it’s a little silly to “put” those words somewhere)
Or rather, Volapukio
The easiest thing to do is to understand the roots of your language. After starting to learn the origin of french words and learning a bit of latin here and there, I suddenly realized how much more I understand about my vocabulary. Then, while learning spanish it suddenly came to me how much easier it was to remember words that had somewhat a reference to french.
Something that largely affects vocabulary is cultural differences and your environments. When learning a language such as japanese, you’ll tend to forget some of those important words because you can’t relate to their meaning as easily and understanding someone using such different words than you know is quite the challenge.
The lack of relation to the sound of one’s own native language is not the only problem entailed by the study of Japanese. In fact, learning a new word in a language whose script is spelt with individual letters or syllables implies memorizing a 2-way scheme such as:
spelling (and pronounciation) + meaning
Instead learning a new glyph – this has to be done before learning the words spelt with it – implies a 3-way scheme such as:
spelling (i.e. the glyph’s shape) + reading(s) + meaning(s)
For words spelt with letters or syllables, only one pronounciation is possible (exceptions are really very scarce). Instead when glyphs are used, the pronounciation or, better, the readings (in some cases up to eight or more) represent a completely independent parameter, because most of them are shared by several completely different glyphs (yet very rarely all of them are in common). And since these sounds have no connection with the equivalent words in Western languages, a good deal of associations is necessary for memorizing them, until with use or rehearsing they become almost automatic; but as associations fade, they can also be very easily forgotten (see my other post in http://www.omniglot.com/blog/2006/04/05/writing-and-memory/ ).
The degree of complexity of the 2-way and 3-way schemes is more or less like switching from a bidimensional world to a three-dimensional one.
Many Western learners of Japanese study this language aiming at being able to speak only, which does not require the knowledge of glyphs; using a romanized spelling, also Japanese falls into the 2-way scheme. But a paradox is that the many homophones (which are typical of languages with an ideographic script) make a written text in romanized Japanese way more difficult to understand, unless one already has a good vocabulary, while for those who need a dictionary, glyphs provide a crucial visual clue.