Nikopol

As a linguist fluent in Korean and Japanese, I give this advice:

It is not necessary to know Japanese.
Just know where your center is.

If you do understand Japanese you will be able to hear many ideas directly from excellent sources. Will that help you? Thats up to how creatively you process the information.

Do learn the names of the techniques in Japanese and what they mean. Make this technical vocabulary your entry point, rather than trying to gobble up the entire language.

If you do decide to study Japanese, remember that one would not expect to learn to swim in a bathtub. Short of coming to Japan, your best bet would be a University course.

As for the building block analogy - it applies to both Japanese and English. In anything you learn a piece and another piece, and then start to fill in the gaps. Kind of like a bittorrent download. But this probably applies to Japanese more than English because English is full of nonstandard pronunciations and conjugations. So think of English as a building block language where you need to apply a lot of sandpaper. Trust that in Japanese it all just fits.

But to repeat, I don't think Japanese is as important in practicing Aikido as is proper breathing, centering and lots of practice with a bokken.