Appropriation happens when the culture is non-dominant and the use of the cultural object tends toward belittling the culture from which it derived. You are fair to say Swahili is non-dominant, and Japanese is going to be a judgement call in the audience. As to belittling, the technical definition of appropriation is defined by the author's use of the object;
in a way that doesn't respect their original meaning, give credit to their source, or reinforces stereotypes or contributes to oppression.
Let's say, for example, your species uses a slang word "Shay-shay!" On it's own, this is not cultural appropriation of the Chinese language "thank you." It will become appropriation only after you use it as described above. Some examples:
Reikoo flipped up his hoodie as he turned to the door. "Shay-shay friend, we'll see ya 'round." He had gotten what he wanted, now the games begin.
"Shay-shay flesh bag,"—a term he picked up in Chinatown was his go-to for put-downs—"looks like you've gotten into a Bad Day."
"Dude's skipped out on a shay-shay, book it down to the station and head 'im off. He's done!" Seemed like Chinese ran all the trolleys in this town. They're so damned polite, boss dropped to just calling them shay-shays.
"Have you got any money left? I REALLY wanted to try a shay-shay before we left town!" Reikoo's sweet tooth was apparently tingling for the local sweet tart at the Ilyan bakery. Not a good time for it, plane leaves in 45 minutes.
Consider the use of the word in these four examples.
- The first example uses the word to say "thank you," exactly as the word is intended. This is not cultural appropriation.
- The second use also uses it to mean "thank you" but in a derogatory way. However, it gives credit to Chinatown as the source. This is not appropriation.
- The third example uses the word in an entirely different way than intended, however it ridicules the Chinese trolly operators as overly "polite." This is cultural appropriation.
- The fourth example uses the word in a completely different way from the original, and gives no credit to a chinese origin, however, it does not express anything at all related to the Chinese culture. From this context it can not be said that "thank you" was the original meaning, it can simply be a coincidence that it has the same sound. This is not objectively cultural appropriation however some readers may interpret it as such because it's origin is vague (or completely absent).
Readers will fill in the blanks. Controversial content should not have blanks around them if you want to avoid the debate about origins; spell it out somewhere in the narrative. For the last example, maybe earlier in the narrative you ran the following:
We stopped into Reikoo's favorite bakery and even from the street we could here the "shay-shay" sound of the confectioner's can of jimmys, which he shook vigorously before dropping them into the delicious treat. Just the sound make your mouth water! The treat was simply called a shay-shay, conveniently enough.
No one will ever accuse you of appropriation with this clearly spelled out. Obviously, Chinese had nothing to do with it. For your 'eechi,' eliminate doubt by painting the non-Japanese word origin into the narrative anywhere. Just a single sentence will do it.
Remember, as an author you are deliberately pulling pictures out of people's heads. When you aren't in control of the pictures you make, then they are. An author's biggest responsibility is not to be understood; it is to not be misunderstood.