Translation:I do not understand Japanese.
That is wonderfully useful to know, thank you. The one time I was in Japan, several years ago, I know that I was using it with wo all the time. Do many verbs take only a specific set of particles like that? It might actually help me to remember them, as I remember Indoeuropean verbs that take a dative or genitive in a language.
わかる(分かる) is closer in meaning to "to break down" than "to understand". If you think of this sentence as "Japanese breaks down for me, you'll start to get a better picture for why が is used here. "Japanese", using が, is the subject, so is the thing carrying out the verb 分かる, as opposed to being the object, the thing the verb is being carried out on.
If you are wondering why "to break down" or "to split up" is used to mean "to understand", think of it as breaking down a complex puzzle into smaller peices to better understand it.
Look up the kanji 分 in a Japanese disctionary and you should be able to see what I mean.
Yeah pretty sure this is right on! When something is intransitive (no direct object), が (or は) is used. For example, 'the door is open' (ドアが開いている) is intransitive with only a subject (the door) and no direct object, while 'I am opening the door' ([私は]ドアを開けている) is transitive, with a subject (me) and direct object (the door) [note that there are slightly different verbs for 'to be open' and 'to open'). It helps me personally to think of intransitive as a state of being (like for 分かる, understanding, or the door being open), and transitive as someone doing something to something (someone opening the door). Pretty sure there are exceptions, but hopefully this is helpful! ^_^