"I want a medium soda."

Translation: Makemake au i ke koloaka lōpū.

[CATipton]

"ke" translates to "the", doesn't it?

[KiUlv]

yes, but in cases like this you need it anyway

[AlanFasick]

Would "Makemake au i hoʻokahi koloaka lōpū." also work?

[HklaniClee]

That would work, but a more common choice would probably be: "Makemake au i kekahi koloaka lōpū."

And a shorter version--which DL just accepted--is: Makemake au i koloaka lōpū. (7/25/2020)