For some purposes, you can function fairly well with material in another language, so long as the topic stays within domains that are familiar to you — like linguistics, say. But when you wander into other domains, especially those that are closely tied to sociocultural conventions, things get messy, even if you stick to nouns; there’s just so much to know about cultural artifacts and customs, for example, and a huge vocabulary to acquire in these areas, in the names of animals and plants, etc.
I can deal pretty well with technical material in French, for example, but I’m easily stumped when it comes to artifacts, animals, plants, and the like. By way of illustration: my daughter gave me a big box of postcards on The Art of Instruction, with images of school materials from the 1950s, from mostly French but also some German sources. The German items have no text, but the French material (from Éditions Rossignol — the name is great; rossignol means ‘nightingale’) is heavy with text. For animals and plants, much of the vocabulary is technical teminology from zoology, anatomy, or botany, and that’s fascinating, but I can’t be expected to know these expressions. However, there are also the common names for animals and plants, and they contain many surprises.
That brings me to the tadpole.