So I'm wondering, while language is obviously not mandatory for learning a martial art, do you think it would be helpful for a beginner to learn some basic Japanese (say thank you, and the numbers from 1 to 10) prior to joining a class? And if so, besides the terminology for aikido techniques, is there anything else in Japanese that would be helpful to learn?
No, it's not really necessary to learn some basic Japanese before you start. Because you don't necessarily know which terms and phrases are important to know until you start. Once you start you'll learn quickly what you need to know even though you won't learn it right away.
I guess, my point is you don't have to worry that much about it just start taking classes.